Intrinsic PN Junction Formation

The body diode in a MOSFET is an inherent consequence of the device's physical structure, arising from the PN junction formed between the source and drain regions. In an N-channel MOSFET, the P-type body (or substrate) and the N+ source/drain regions create a parasitic PN diode. This diode exhibits standard PN junction behavior but with critical implications for MOSFET operation in switching applications.

Physical Structure and Doping Profiles

The PN junction forms due to the doping contrast between:

• N+ regions: Heavily doped silicon (≈10¹⁹ cm^-3) forming source and drain
• P-type body: Lightly to moderately doped substrate (≈10¹⁵-10¹⁷ cm^-3)

The abrupt doping transition creates a depletion region governed by Poisson's equation:

where φ is the electrostatic potential, ρ(x) is the charge density, and ε_si is silicon's permittivity.

Depletion Region Characteristics

At zero bias, the depletion width W extends asymmetrically:

where N_A and N_D are acceptor/donor concentrations, and φ_bi is the built-in potential:

Forward and Reverse Bias Behavior

Under forward bias (V_DS < 0 for N-MOSFET):

• Depletion region narrows
• Current follows Shockley diode equation:

Under reverse bias (V_DS > 0):

• Depletion region widens
• Leakage current dominated by generation-recombination

Practical Implications in MOSFET Operation

The body diode becomes consequential in:

• Synchronous rectification (third-quadrant operation)
• Inductive load switching (freewheeling current path)
• Reverse recovery effects during fast switching

The diode's reverse recovery charge (Q_rr) directly impacts switching losses in power electronics applications, with:

where τ_s and τ_t are storage and transit times respectively.

1.2 Structural Origin in Power MOSFETs

The body diode in a power MOSFET is an intrinsic consequence of the device's physical construction. Unlike discrete diodes, which are intentionally fabricated as PN junctions, the body diode arises unavoidably due to the doping profiles and semiconductor layers required for MOSFET operation.

Doping Profile and Junction Formation

In an N-channel enhancement-mode power MOSFET, the device structure consists of:

• An N+ doped source region
• A P-doped body region
• An N- doped drift region (for high voltage blocking)
• An N+ doped drain region

The critical PN junction forming the body diode exists between the P-body and N- drift regions. This junction is forward-biased when the drain potential falls below the source potential by approximately 0.7V (for silicon).

Vertical vs. Lateral Structures

In vertical DMOS structures (common in power MOSFETs), the current flows vertically through the device, with the body diode formed between the P-body and N-epitaxial layer. The doping concentration gradient affects both the diode's forward voltage drop and reverse recovery characteristics:

where I_S is the saturation current determined by the doping concentrations:

Parasitic Bipolar Transistor Implications

The same P-body/N-drift junction that forms the body diode also creates a parasitic NPN bipolar transistor (with source as emitter, body as base, and drain as collector). This has important consequences for:

• Unclamped inductive switching (UIS) capability
• Safe operating area (SOA) limitations
• Potential for latch-up during reverse conduction

The doping profile must be carefully optimized to balance body diode performance with MOSFET characteristics. Higher P-body doping reduces parasitic bipolar gain but increases diode forward voltage.

Modern Design Trade-offs

Advanced power MOSFET technologies employ various techniques to manage body diode behavior:

• Charge balance techniques (e.g., superjunction MOSFETs) that modify the drift region doping
• Lifetime killing to improve reverse recovery time at the expense of increased V_F
• Trench gate structures that alter the current path during diode conduction

The figure below shows a cross-section of a typical power MOSFET highlighting the body diode formation:

1.2 Structural Origin in Power MOSFETs

The body diode in a power MOSFET is an intrinsic consequence of the device's physical construction. Unlike discrete diodes, which are intentionally fabricated as PN junctions, the body diode arises unavoidably due to the doping profiles and semiconductor layers required for MOSFET operation.

Doping Profile and Junction Formation

In an N-channel enhancement-mode power MOSFET, the device structure consists of:

• An N+ doped source region
• A P-doped body region
• An N- doped drift region (for high voltage blocking)
• An N+ doped drain region

The critical PN junction forming the body diode exists between the P-body and N- drift regions. This junction is forward-biased when the drain potential falls below the source potential by approximately 0.7V (for silicon).

Vertical vs. Lateral Structures

In vertical DMOS structures (common in power MOSFETs), the current flows vertically through the device, with the body diode formed between the P-body and N-epitaxial layer. The doping concentration gradient affects both the diode's forward voltage drop and reverse recovery characteristics:

where I_S is the saturation current determined by the doping concentrations:

Parasitic Bipolar Transistor Implications

The same P-body/N-drift junction that forms the body diode also creates a parasitic NPN bipolar transistor (with source as emitter, body as base, and drain as collector). This has important consequences for:

• Unclamped inductive switching (UIS) capability
• Safe operating area (SOA) limitations
• Potential for latch-up during reverse conduction

The doping profile must be carefully optimized to balance body diode performance with MOSFET characteristics. Higher P-body doping reduces parasitic bipolar gain but increases diode forward voltage.

Modern Design Trade-offs

Advanced power MOSFET technologies employ various techniques to manage body diode behavior:

• Charge balance techniques (e.g., superjunction MOSFETs) that modify the drift region doping
• Lifetime killing to improve reverse recovery time at the expense of increased V_F
• Trench gate structures that alter the current path during diode conduction

The figure below shows a cross-section of a typical power MOSFET highlighting the body diode formation:

1.3 Polarity and Terminal Connections

Intrinsic Diode Formation in MOSFETs

The body diode in a MOSFET is an inherent consequence of its physical structure, formed by the p-n junction between the body (substrate) and the drain regions. In an n-channel MOSFET, the p-type body and n-type drain create a diode with the anode at the body (source terminal in standard configurations) and the cathode at the drain. For p-channel MOSFETs, the polarity reverses: the n-type body and p-type drain form a diode with the anode at the drain and the cathode at the source.

Terminal Voltage Polarities

The body diode conducts when the voltage across it exceeds its forward bias threshold (typically 0.7 V for silicon). For an n-channel MOSFET:

• Forward bias: Source (body) at higher potential than drain (V_DS < 0).
• Reverse bias: Drain at higher potential than source (V_DS > 0).

In p-channel devices, the conditions invert. This behavior critically impacts switching applications, where unintended diode conduction can lead to shoot-through currents in bridge circuits.

Mathematical Modeling of Forward Bias

The diode current I_D follows the Shockley diode equation:

where:

• I_S = reverse saturation current (~1 nA to 1 µA for power MOSFETs)
• V_D = forward voltage across the diode
• n = ideality factor (1.0 to 2.0)
• V_T = thermal voltage (≈26 mV at 300 K)

Practical Implications in Circuit Design

In synchronous buck converters, the body diode conducts during dead-time intervals between high-side and low-side MOSFET switching. Designers must account for:

• Reverse recovery charge (Q_rr): Causes power loss during diode turn-off, calculated as:

• Conduction losses: Power dissipation during forward conduction (P_cond = V_F × I_D).

Parasitic BJT Activation Risk

If the body diode forward bias exceeds ≈0.7 V, the parasitic bipolar junction transistor (BJT) formed by the drain (collector), body (base), and source (emitter) may activate, leading to:

• Latch-up conditions in CMOS circuits
• Uncontrollable current flow
• Device failure due to thermal runaway

Modern MOSFET designs mitigate this through heavy body doping and careful layout to reduce the body resistance (R_B).

1.3 Polarity and Terminal Connections

Intrinsic Diode Formation in MOSFETs

The body diode in a MOSFET is an inherent consequence of its physical structure, formed by the p-n junction between the body (substrate) and the drain regions. In an n-channel MOSFET, the p-type body and n-type drain create a diode with the anode at the body (source terminal in standard configurations) and the cathode at the drain. For p-channel MOSFETs, the polarity reverses: the n-type body and p-type drain form a diode with the anode at the drain and the cathode at the source.

Terminal Voltage Polarities

The body diode conducts when the voltage across it exceeds its forward bias threshold (typically 0.7 V for silicon). For an n-channel MOSFET:

• Forward bias: Source (body) at higher potential than drain (V_DS < 0).
• Reverse bias: Drain at higher potential than source (V_DS > 0).

In p-channel devices, the conditions invert. This behavior critically impacts switching applications, where unintended diode conduction can lead to shoot-through currents in bridge circuits.

Mathematical Modeling of Forward Bias

The diode current I_D follows the Shockley diode equation:

where:

• I_S = reverse saturation current (~1 nA to 1 µA for power MOSFETs)
• V_D = forward voltage across the diode
• n = ideality factor (1.0 to 2.0)
• V_T = thermal voltage (≈26 mV at 300 K)

Practical Implications in Circuit Design

In synchronous buck converters, the body diode conducts during dead-time intervals between high-side and low-side MOSFET switching. Designers must account for:

• Reverse recovery charge (Q_rr): Causes power loss during diode turn-off, calculated as:

• Conduction losses: Power dissipation during forward conduction (P_cond = V_F × I_D).

Parasitic BJT Activation Risk

If the body diode forward bias exceeds ≈0.7 V, the parasitic bipolar junction transistor (BJT) formed by the drain (collector), body (base), and source (emitter) may activate, leading to:

• Latch-up conditions in CMOS circuits
• Uncontrollable current flow
• Device failure due to thermal runaway

Modern MOSFET designs mitigate this through heavy body doping and careful layout to reduce the body resistance (R_B).

Forward Voltage Drop (V_F)

The intrinsic body diode in a MOSFET exhibits a forward voltage drop (V_F) when conducting current in the third quadrant of operation. This behavior stems from the p-n junction formed between the body (p-type substrate) and drain (n-type epitaxial layer) in an n-channel MOSFET.

Physics of V_F in the Body Diode

The forward voltage arises from the built-in potential (V_bi) of the p-n junction and the resistive voltage drop across the drift region. The total V_F can be expressed as:

Where:

• V_bi is the built-in potential (typically 0.6-0.8V for silicon)
• I_F is the forward current
• R_drift is the resistance of the lightly doped drift region
• n is the ideality factor (1-2)
• I_S is the reverse saturation current

Temperature Dependence

The forward voltage exhibits a negative temperature coefficient due to two competing effects:

Where E_g is the semiconductor bandgap. The temperature coefficient typically ranges from -1 mV/°C to -2 mV/°C for silicon MOSFETs.

Practical Implications in Power Circuits

In synchronous buck converters, the body diode conducts during dead-time intervals. The forward voltage drop directly impacts:

• Conduction losses during dead-time
• Reverse recovery characteristics
• Thermal management requirements

Modern power MOSFETs often optimize the body diode through:

• Lifetime control techniques to reduce reverse recovery charge
• Advanced doping profiles to minimize R_drift
• Trench gate structures that modify current spreading

Forward Voltage Drop (V_F)

The intrinsic body diode in a MOSFET exhibits a forward voltage drop (V_F) when conducting current in the third quadrant of operation. This behavior stems from the p-n junction formed between the body (p-type substrate) and drain (n-type epitaxial layer) in an n-channel MOSFET.

Physics of V_F in the Body Diode

The forward voltage arises from the built-in potential (V_bi) of the p-n junction and the resistive voltage drop across the drift region. The total V_F can be expressed as:

Where:

• V_bi is the built-in potential (typically 0.6-0.8V for silicon)
• I_F is the forward current
• R_drift is the resistance of the lightly doped drift region
• n is the ideality factor (1-2)
• I_S is the reverse saturation current

Temperature Dependence

The forward voltage exhibits a negative temperature coefficient due to two competing effects:

Where E_g is the semiconductor bandgap. The temperature coefficient typically ranges from -1 mV/°C to -2 mV/°C for silicon MOSFETs.

Practical Implications in Power Circuits

In synchronous buck converters, the body diode conducts during dead-time intervals. The forward voltage drop directly impacts:

• Conduction losses during dead-time
• Reverse recovery characteristics
• Thermal management requirements

Modern power MOSFETs often optimize the body diode through:

• Lifetime control techniques to reduce reverse recovery charge
• Advanced doping profiles to minimize R_drift
• Trench gate structures that modify current spreading

2.2 Reverse Recovery Behavior

The intrinsic body diode of a MOSFET exhibits reverse recovery behavior when transitioning from forward conduction to reverse blocking. This phenomenon arises due to the stored minority charge in the diode's drift region, which must be removed before the diode can block reverse voltage. The reverse recovery process introduces switching losses and can lead to voltage spikes, making it critical to model accurately in high-frequency power electronics.

Mechanism of Reverse Recovery

When the body diode is forward-biased, electrons and holes are injected into the drift region, creating a stored charge Q_rr. Upon reverse bias application, this charge must be extracted before the diode can block voltage. The reverse recovery current I_rr flows in the opposite direction until the stored charge is depleted. The process consists of two phases:

• Soft Recovery Phase: The diode current decreases as carriers recombine.
• Snap-off Phase: The remaining charge is rapidly swept out, causing a sharp current cutoff.

Mathematical Modeling

The reverse recovery charge Q_rr is derived from the diode's minority carrier lifetime τ and forward current I_F:

The peak reverse recovery current I_rr depends on the di/dt rate during turn-off:

where di/dt is the rate of current change. The reverse recovery time t_rr is given by:

Impact on Circuit Design

Reverse recovery induces:

• Switching Losses: Energy dissipation during charge extraction increases converter losses.
• Voltage Overshoot: Rapid current cutoff (snap-off) can excite parasitic inductances, leading to destructive voltage spikes.
• EMI: High-frequency ringing from abrupt transitions worsens electromagnetic interference.

Mitigation Techniques

To minimize reverse recovery effects:

• SiC/GaN MOSFETs: Wider bandgap materials reduce stored charge due to higher critical field strength.
• Snubber Circuits: RC networks dampen voltage transients.
• Synchronous Rectification: Actively turn on the MOSFET channel to bypass the body diode.

2.2 Reverse Recovery Behavior

The intrinsic body diode of a MOSFET exhibits reverse recovery behavior when transitioning from forward conduction to reverse blocking. This phenomenon arises due to the stored minority charge in the diode's drift region, which must be removed before the diode can block reverse voltage. The reverse recovery process introduces switching losses and can lead to voltage spikes, making it critical to model accurately in high-frequency power electronics.

Mechanism of Reverse Recovery

When the body diode is forward-biased, electrons and holes are injected into the drift region, creating a stored charge Q_rr. Upon reverse bias application, this charge must be extracted before the diode can block voltage. The reverse recovery current I_rr flows in the opposite direction until the stored charge is depleted. The process consists of two phases:

• Soft Recovery Phase: The diode current decreases as carriers recombine.
• Snap-off Phase: The remaining charge is rapidly swept out, causing a sharp current cutoff.

Mathematical Modeling

The reverse recovery charge Q_rr is derived from the diode's minority carrier lifetime τ and forward current I_F:

The peak reverse recovery current I_rr depends on the di/dt rate during turn-off:

where di/dt is the rate of current change. The reverse recovery time t_rr is given by:

Impact on Circuit Design

Reverse recovery induces:

• Switching Losses: Energy dissipation during charge extraction increases converter losses.
• Voltage Overshoot: Rapid current cutoff (snap-off) can excite parasitic inductances, leading to destructive voltage spikes.
• EMI: High-frequency ringing from abrupt transitions worsens electromagnetic interference.

Mitigation Techniques

To minimize reverse recovery effects:

• SiC/GaN MOSFETs: Wider bandgap materials reduce stored charge due to higher critical field strength.
• Snubber Circuits: RC networks dampen voltage transients.
• Synchronous Rectification: Actively turn on the MOSFET channel to bypass the body diode.

2.3 Temperature Dependency

The intrinsic body diode of a MOSFET exhibits significant temperature-dependent characteristics, primarily due to the thermal sensitivity of semiconductor material properties. These effects are critical in power electronics applications where self-heating and ambient temperature variations influence device reliability.

Forward Voltage Drop (V_F) Variation

The forward voltage drop of the body diode decreases with increasing temperature, governed by the temperature dependence of the intrinsic carrier concentration (n_i) and carrier mobility. The relationship can be derived from the diode current equation:

where the saturation current I_S(T) is temperature-dependent:

The intrinsic carrier concentration follows:

where E_g is the temperature-dependent bandgap energy. For silicon, E_g decreases approximately linearly with temperature:

with typical values for silicon being E_g0 = 1.17 eV, α = 4.73×10^-4 eV/K, and β = 636 K.

Reverse Recovery Characteristics

Temperature significantly impacts the reverse recovery charge (Q_rr) and time (t_rr). The minority carrier lifetime (τ) increases with temperature, leading to greater stored charge:

where γ typically ranges between 1.5 and 2.5 for silicon devices. This results in higher switching losses at elevated temperatures.

Thermal Runaway Considerations

In synchronous rectification applications, the body diode's negative temperature coefficient of forward voltage can lead to thermal instability if:

• The diode conducts significant current during dead-time intervals
• Parallel MOSFETs share current unevenly
• The system lacks proper thermal management

The stability condition requires:

where R_th(j-a) is the junction-to-ambient thermal resistance.

Practical Implications

Modern power MOSFET datasheets typically specify body diode parameters at multiple temperatures (25°C, 125°C). Key design considerations include:

• Derating of current capability at high temperatures
• Increased switching losses in high-frequency applications
• Potential for current hogging in parallel devices
• Need for temperature-compensated gate drive timing

2.3 Temperature Dependency

The intrinsic body diode of a MOSFET exhibits significant temperature-dependent characteristics, primarily due to the thermal sensitivity of semiconductor material properties. These effects are critical in power electronics applications where self-heating and ambient temperature variations influence device reliability.

Forward Voltage Drop (V_F) Variation

The forward voltage drop of the body diode decreases with increasing temperature, governed by the temperature dependence of the intrinsic carrier concentration (n_i) and carrier mobility. The relationship can be derived from the diode current equation:

where the saturation current I_S(T) is temperature-dependent:

The intrinsic carrier concentration follows:

where E_g is the temperature-dependent bandgap energy. For silicon, E_g decreases approximately linearly with temperature:

with typical values for silicon being E_g0 = 1.17 eV, α = 4.73×10^-4 eV/K, and β = 636 K.

Reverse Recovery Characteristics

Temperature significantly impacts the reverse recovery charge (Q_rr) and time (t_rr). The minority carrier lifetime (τ) increases with temperature, leading to greater stored charge:

where γ typically ranges between 1.5 and 2.5 for silicon devices. This results in higher switching losses at elevated temperatures.

Thermal Runaway Considerations

In synchronous rectification applications, the body diode's negative temperature coefficient of forward voltage can lead to thermal instability if:

• The diode conducts significant current during dead-time intervals
• Parallel MOSFETs share current unevenly
• The system lacks proper thermal management

The stability condition requires:

where R_th(j-a) is the junction-to-ambient thermal resistance.

Practical Implications

Modern power MOSFET datasheets typically specify body diode parameters at multiple temperatures (25°C, 125°C). Key design considerations include:

• Derating of current capability at high temperatures
• Increased switching losses in high-frequency applications
• Potential for current hogging in parallel devices
• Need for temperature-compensated gate drive timing

3.1 Conduction During Dead-Time in Bridge Circuits

In bridge circuits such as H-bridges or half-bridge configurations, dead-time is intentionally introduced between the turn-off of one MOSFET and the turn-on of its complementary device to prevent shoot-through currents. During this interval, inductive load currents must find a conduction path, and the body diodes of the MOSFETs play a critical role in enabling freewheeling.

Mechanism of Body Diode Conduction

When the high-side MOSFET turns off, the inductor current cannot abruptly stop. Instead, it commutates to the body diode of the low-side MOSFET (or vice versa). The forward voltage drop (V_SD) of the body diode determines the energy dissipation during this period. For a standard silicon MOSFET, this drop is typically 0.7–1.2 V, while in SiC or GaN devices, it may exceed 2–3 V due to higher built-in potentials.

where V_th is the diode threshold voltage, I_D is the conducted current, and R_SD is the series resistance of the diode.

Impact on Switching Losses

Dead-time conduction introduces additional losses proportional to the diode's forward voltage and the duration of dead-time (t_dead):

where f_sw is the switching frequency. These losses become significant in high-frequency applications (>100 kHz), necessitating careful dead-time optimization or synchronous rectification techniques.

Reverse Recovery and Its Consequences

The body diode's reverse recovery charge (Q_rr) becomes critical during the turn-on of the complementary MOSFET. A finite Q_rr leads to a transient current spike, increasing switching losses and EMI. For SiC MOSFETs, the absence of minority carriers reduces Q_rr, making them preferable for high-efficiency designs.

Practical Mitigation Strategies

• Minimizing Dead-Time: Reducing t_dead lowers losses but risks shoot-through. Advanced gate drivers with adaptive dead-time control dynamically adjust this interval.
• External Schottky Diodes: Parallel Schottky diodes with lower V_F can bypass the body diode, reducing conduction losses.
• Synchronous Rectification: Actively turning on the low-side MOSFET during dead-time exploits its channel resistance (R_DS(on)) instead of the diode drop.

3.1 Conduction During Dead-Time in Bridge Circuits

In bridge circuits such as H-bridges or half-bridge configurations, dead-time is intentionally introduced between the turn-off of one MOSFET and the turn-on of its complementary device to prevent shoot-through currents. During this interval, inductive load currents must find a conduction path, and the body diodes of the MOSFETs play a critical role in enabling freewheeling.

Mechanism of Body Diode Conduction

When the high-side MOSFET turns off, the inductor current cannot abruptly stop. Instead, it commutates to the body diode of the low-side MOSFET (or vice versa). The forward voltage drop (V_SD) of the body diode determines the energy dissipation during this period. For a standard silicon MOSFET, this drop is typically 0.7–1.2 V, while in SiC or GaN devices, it may exceed 2–3 V due to higher built-in potentials.

where V_th is the diode threshold voltage, I_D is the conducted current, and R_SD is the series resistance of the diode.

Impact on Switching Losses

Dead-time conduction introduces additional losses proportional to the diode's forward voltage and the duration of dead-time (t_dead):

where f_sw is the switching frequency. These losses become significant in high-frequency applications (>100 kHz), necessitating careful dead-time optimization or synchronous rectification techniques.

Reverse Recovery and Its Consequences

The body diode's reverse recovery charge (Q_rr) becomes critical during the turn-on of the complementary MOSFET. A finite Q_rr leads to a transient current spike, increasing switching losses and EMI. For SiC MOSFETs, the absence of minority carriers reduces Q_rr, making them preferable for high-efficiency designs.

Practical Mitigation Strategies

• Minimizing Dead-Time: Reducing t_dead lowers losses but risks shoot-through. Advanced gate drivers with adaptive dead-time control dynamically adjust this interval.
• External Schottky Diodes: Parallel Schottky diodes with lower V_F can bypass the body diode, reducing conduction losses.
• Synchronous Rectification: Actively turning on the low-side MOSFET during dead-time exploits its channel resistance (R_DS(on)) instead of the diode drop.

3.2 Unclamped Inductive Load Switching

When a MOSFET switches off an inductive load without a freewheeling diode, the stored energy in the inductor forces current through the body diode. This results in a voltage spike across the MOSFET, governed by:

where L is the inductance, di/dt is the current decay rate, and R_DS(on) is the MOSFET’s on-state resistance. The body diode’s reverse recovery charge (Q_rr) further exacerbates losses:

Reverse Recovery Dynamics

The body diode’s minority carriers recombine during turn-off, causing a transient reverse current (I_rr). This phenomenon is modeled by:

where I_F is the forward current before switch-off and τ is the carrier lifetime. Fast-recovery diodes mitigate this by reducing τ.

Practical Implications

• Voltage Overshoot: Unclamped switching can exceed the MOSFET’s V_DSS rating, leading to avalanche breakdown.
• Thermal Stress: Reverse recovery losses increase junction temperature, risking thermal runaway.
• Snubber Circuits: RC networks or Zener clamps are often added to dissipate inductive energy safely.

SPICE Simulation Example

The following circuit demonstrates unclamped switching effects:

Key observations from simulation:

• Peak V_DS correlates with L·di/dt.
• Body diode conduction lasts until I_LOAD reaches zero.

3.2 Unclamped Inductive Load Switching

When a MOSFET switches off an inductive load without a freewheeling diode, the stored energy in the inductor forces current through the body diode. This results in a voltage spike across the MOSFET, governed by:

where L is the inductance, di/dt is the current decay rate, and R_DS(on) is the MOSFET’s on-state resistance. The body diode’s reverse recovery charge (Q_rr) further exacerbates losses:

Reverse Recovery Dynamics

The body diode’s minority carriers recombine during turn-off, causing a transient reverse current (I_rr). This phenomenon is modeled by:

where I_F is the forward current before switch-off and τ is the carrier lifetime. Fast-recovery diodes mitigate this by reducing τ.

Practical Implications

• Voltage Overshoot: Unclamped switching can exceed the MOSFET’s V_DSS rating, leading to avalanche breakdown.
• Thermal Stress: Reverse recovery losses increase junction temperature, risking thermal runaway.
• Snubber Circuits: RC networks or Zener clamps are often added to dissipate inductive energy safely.

SPICE Simulation Example

The following circuit demonstrates unclamped switching effects:

Key observations from simulation:

• Peak V_DS correlates with L·di/dt.
• Body diode conduction lasts until I_LOAD reaches zero.

Third-Quadrant Operation

In power electronics, the third-quadrant operation of a MOSFET refers to the condition where the drain-source voltage (V_DS) is negative while the gate-source voltage (V_GS) is below the threshold. This mode is critical in synchronous rectification, motor drives, and bidirectional converters, where the intrinsic body diode conducts before the channel is actively inverted.

Conduction Mechanisms

When V_DS < 0 and V_GS < V_th, the MOSFET operates in the third quadrant. The body diode, formed by the p-n junction between the source (p-body) and drain (n-epitaxial layer), becomes forward-biased. The current flows through this diode, exhibiting a voltage drop (V_SD) governed by the Shockley diode equation:

where I_S is the reverse saturation current, n is the ideality factor, and V_T = kT/q is the thermal voltage. For silicon MOSFETs, V_SD typically ranges from 0.7 V to 1.5 V, depending on doping concentrations and temperature.

Impact of Channel Inversion

If V_GS exceeds the threshold voltage while V_DS remains negative, the MOSFET enters synchronous conduction. The channel inverts, providing a parallel low-resistance path (R_DS(on)) for current. The total current splits between the body diode and the channel, reducing conduction losses. The equivalent resistance is:

where R_diode = dV_SD/dI_D is the dynamic resistance of the body diode.

Reverse Recovery and Switching Losses

The body diode exhibits reverse recovery when V_DS transitions from negative to positive. Stored minority carriers in the diode’s depletion region must recombine, causing a transient reverse current (I_RR) and energy loss (E_RR):

Here, Q_RR is the reverse recovery charge, a key figure of merit for high-frequency applications. Modern MOSFETs optimize this by reducing minority carrier lifetime (e.g., through platinum or electron irradiation doping).

Practical Considerations

• Dead-time management: In bridge circuits, a delay between turning off one MOSFET and turning on its complement prevents shoot-through but must minimize body diode conduction time to reduce losses.
• Thermal effects: The body diode’s forward drop increases with temperature, exacerbating conduction losses in high-power designs.
• Alternative topologies: SiC and GaN MOSFETs integrate Schottky barrier diodes to eliminate reverse recovery, improving efficiency in high-frequency converters.

Third-Quadrant Operation

In power electronics, the third-quadrant operation of a MOSFET refers to the condition where the drain-source voltage (V_DS) is negative while the gate-source voltage (V_GS) is below the threshold. This mode is critical in synchronous rectification, motor drives, and bidirectional converters, where the intrinsic body diode conducts before the channel is actively inverted.

Conduction Mechanisms

When V_DS < 0 and V_GS < V_th, the MOSFET operates in the third quadrant. The body diode, formed by the p-n junction between the source (p-body) and drain (n-epitaxial layer), becomes forward-biased. The current flows through this diode, exhibiting a voltage drop (V_SD) governed by the Shockley diode equation:

where I_S is the reverse saturation current, n is the ideality factor, and V_T = kT/q is the thermal voltage. For silicon MOSFETs, V_SD typically ranges from 0.7 V to 1.5 V, depending on doping concentrations and temperature.

Impact of Channel Inversion

If V_GS exceeds the threshold voltage while V_DS remains negative, the MOSFET enters synchronous conduction. The channel inverts, providing a parallel low-resistance path (R_DS(on)) for current. The total current splits between the body diode and the channel, reducing conduction losses. The equivalent resistance is:

where R_diode = dV_SD/dI_D is the dynamic resistance of the body diode.

Reverse Recovery and Switching Losses

The body diode exhibits reverse recovery when V_DS transitions from negative to positive. Stored minority carriers in the diode’s depletion region must recombine, causing a transient reverse current (I_RR) and energy loss (E_RR):

Here, Q_RR is the reverse recovery charge, a key figure of merit for high-frequency applications. Modern MOSFETs optimize this by reducing minority carrier lifetime (e.g., through platinum or electron irradiation doping).

Practical Considerations

• Dead-time management: In bridge circuits, a delay between turning off one MOSFET and turning on its complement prevents shoot-through but must minimize body diode conduction time to reduce losses.
• Thermal effects: The body diode’s forward drop increases with temperature, exacerbating conduction losses in high-power designs.
• Alternative topologies: SiC and GaN MOSFETs integrate Schottky barrier diodes to eliminate reverse recovery, improving efficiency in high-frequency converters.

4.1 Impact on Switching Losses

The intrinsic body diode of a MOSFET plays a significant role in switching losses, particularly during hard-switching and reverse recovery events. These losses arise from the interplay between the diode's stored charge and the transient behavior of the MOSFET during turn-on and turn-off.

Reverse Recovery Losses

When the MOSFET is turned on while the body diode is conducting, the diode must first recover from its forward-biased state before the channel can fully control the current. The reverse recovery process generates a transient current spike, dissipating energy as heat. The power loss due to reverse recovery can be modeled as:

where:

• Q_rr is the reverse recovery charge,
• V_DS is the drain-source voltage,
• f_sw is the switching frequency.

Conduction Losses During Dead Time

In bridge configurations (e.g., half-bridge or full-bridge), dead time is introduced to prevent shoot-through. During this interval, the body diode conducts, leading to additional conduction losses:

where:

• V_F is the forward voltage drop of the body diode,
• I_D is the drain current,
• t_dead is the dead time duration.

Switching Energy Dissipation

The total switching energy (E_sw) is influenced by the body diode's reverse recovery characteristics. A simplified model for turn-on switching loss is:

where t_rr is the reverse recovery time. The integral accounts for the overlap between voltage and current during the switching transient.

Mitigation Techniques

To minimize losses:

• Synchronous rectification: Actively turn on the MOSFET channel instead of relying on the body diode.
• Optimized dead time: Reduce dead time to limit diode conduction while avoiding shoot-through.
• Fast-recovery MOSFETs: Use devices with lower Q_rr to decrease reverse recovery losses.

4.1 Impact on Switching Losses

The intrinsic body diode of a MOSFET plays a significant role in switching losses, particularly during hard-switching and reverse recovery events. These losses arise from the interplay between the diode's stored charge and the transient behavior of the MOSFET during turn-on and turn-off.

Reverse Recovery Losses

When the MOSFET is turned on while the body diode is conducting, the diode must first recover from its forward-biased state before the channel can fully control the current. The reverse recovery process generates a transient current spike, dissipating energy as heat. The power loss due to reverse recovery can be modeled as:

where:

• Q_rr is the reverse recovery charge,
• V_DS is the drain-source voltage,
• f_sw is the switching frequency.

Conduction Losses During Dead Time

In bridge configurations (e.g., half-bridge or full-bridge), dead time is introduced to prevent shoot-through. During this interval, the body diode conducts, leading to additional conduction losses:

where:

• V_F is the forward voltage drop of the body diode,
• I_D is the drain current,
• t_dead is the dead time duration.

Switching Energy Dissipation

The total switching energy (E_sw) is influenced by the body diode's reverse recovery characteristics. A simplified model for turn-on switching loss is:

where t_rr is the reverse recovery time. The integral accounts for the overlap between voltage and current during the switching transient.

Mitigation Techniques

To minimize losses:

• Synchronous rectification: Actively turn on the MOSFET channel instead of relying on the body diode.
• Optimized dead time: Reduce dead time to limit diode conduction while avoiding shoot-through.
• Fast-recovery MOSFETs: Use devices with lower Q_rr to decrease reverse recovery losses.

4.2 Synchronous Rectification Challenges

Reverse Recovery and Dead-Time Conduction

In synchronous rectification, the body diode of a MOSFET conducts during the dead-time interval between high-side and low-side switch transitions. This introduces two primary challenges:

• Reverse recovery charge (Q_rr): When the MOSFET turns on, the body diode must dissipate stored minority carriers, leading to a transient current spike.
• Conduction losses: The diode's forward voltage drop (V_F ≈ 0.7V) dominates during dead-time, reducing efficiency compared to ideal synchronous operation.

Switching Loss Analysis

The reverse recovery process generates switching losses proportional to the recovery charge and DC bus voltage:

where f_sw is the switching frequency. In fast-switching applications (>100kHz), these losses can exceed conduction losses.

Parasitic Inductance Effects

Stray inductance in the commutation loop (L_stray) interacts with di/dt during reverse recovery, causing voltage overshoot:

This necessitates higher voltage-rated MOSFETs or active clamping circuits in high-power designs.

Mitigation Techniques

Advanced synchronous controllers implement strategies to minimize body diode conduction:

• Adaptive dead-time control: Dynamically adjusts timing to minimize diode conduction while preventing shoot-through
• Negative gate drive: Actively pulls the gate below source potential to ensure complete channel turn-off
• SiC/GaN devices: Wide-bandgap MOSFETs exhibit negligible reverse recovery due to unipolar conduction

4.2 Synchronous Rectification Challenges

Reverse Recovery and Dead-Time Conduction

In synchronous rectification, the body diode of a MOSFET conducts during the dead-time interval between high-side and low-side switch transitions. This introduces two primary challenges:

• Reverse recovery charge (Q_rr): When the MOSFET turns on, the body diode must dissipate stored minority carriers, leading to a transient current spike.
• Conduction losses: The diode's forward voltage drop (V_F ≈ 0.7V) dominates during dead-time, reducing efficiency compared to ideal synchronous operation.

Switching Loss Analysis

The reverse recovery process generates switching losses proportional to the recovery charge and DC bus voltage:

where f_sw is the switching frequency. In fast-switching applications (>100kHz), these losses can exceed conduction losses.

Parasitic Inductance Effects

Stray inductance in the commutation loop (L_stray) interacts with di/dt during reverse recovery, causing voltage overshoot:

This necessitates higher voltage-rated MOSFETs or active clamping circuits in high-power designs.

Mitigation Techniques

Advanced synchronous controllers implement strategies to minimize body diode conduction:

• Adaptive dead-time control: Dynamically adjusts timing to minimize diode conduction while preventing shoot-through
• Negative gate drive: Actively pulls the gate below source potential to ensure complete channel turn-off
• SiC/GaN devices: Wide-bandgap MOSFETs exhibit negligible reverse recovery due to unipolar conduction

4.3 Layout Optimization for Diode Performance

The body diode in a MOSFET is inherently formed by the p-n junction between the source and drain regions. Its performance is heavily influenced by the device's physical layout, which affects parameters such as forward voltage drop (V_F), reverse recovery charge (Q_rr), and thermal resistance. Optimizing the layout requires careful consideration of geometric and material factors.

Geometric Considerations

The body diode's forward voltage drop is governed by the current density distribution across the active area. A non-uniform current density leads to localized heating and increased V_F. To mitigate this:

• Increase cell density: A higher number of smaller cells distributes current more evenly, reducing peak current density. However, this increases gate capacitance and switching losses.
• Optimize aspect ratio: A rectangular cell layout (rather than square) can improve current spreading, but must balance against gate resistance effects.

The reverse recovery charge Q_rr is minimized by reducing minority carrier lifetime in the drift region. This can be achieved through:

where q is the electron charge, A is the active area, W_d is the depletion width, and Δp(x) is the excess hole concentration.

Material and Process Optimization

Heavy metal doping (e.g., platinum or gold diffusion) reduces minority carrier lifetime, improving reverse recovery at the cost of increased leakage current. Alternative approaches include:

• Local lifetime killing: Implanting recombination centers only near the body-drain junction preserves other device characteristics.
• Epitaxial layer tuning: Varying doping concentration in the epi-layer can create built-in electric fields that sweep out carriers during reverse recovery.

Thermal Management

The body diode's power dissipation (P_diss) during conduction is:

where I_F is forward current and R_on is the channel resistance. To minimize thermal resistance:

• Place source contacts uniformly across the die to prevent current crowding.
• Use thick top metal layers (≥4μm) for better heat spreading.
• Implement thermal vias under source pads to conduct heat to the package.

Advanced Layout Techniques

Trench MOSFET designs introduce additional considerations:

• Gate trench placement affects the body diode's current path - alternating trench and source stripes can improve performance.
• Superjunction structures require careful balancing of p and n pillar doping to maintain low V_F while achieving fast recovery.

In multi-die paralleled configurations, ensure symmetric layout to current sharing. Even small mismatches in bond wire lengths or die placement can cause significant current imbalance during diode conduction.

4.3 Layout Optimization for Diode Performance

The body diode in a MOSFET is inherently formed by the p-n junction between the source and drain regions. Its performance is heavily influenced by the device's physical layout, which affects parameters such as forward voltage drop (V_F), reverse recovery charge (Q_rr), and thermal resistance. Optimizing the layout requires careful consideration of geometric and material factors.

Geometric Considerations

The body diode's forward voltage drop is governed by the current density distribution across the active area. A non-uniform current density leads to localized heating and increased V_F. To mitigate this:

• Increase cell density: A higher number of smaller cells distributes current more evenly, reducing peak current density. However, this increases gate capacitance and switching losses.
• Optimize aspect ratio: A rectangular cell layout (rather than square) can improve current spreading, but must balance against gate resistance effects.

The reverse recovery charge Q_rr is minimized by reducing minority carrier lifetime in the drift region. This can be achieved through:

where q is the electron charge, A is the active area, W_d is the depletion width, and Δp(x) is the excess hole concentration.

Material and Process Optimization

Heavy metal doping (e.g., platinum or gold diffusion) reduces minority carrier lifetime, improving reverse recovery at the cost of increased leakage current. Alternative approaches include:

• Local lifetime killing: Implanting recombination centers only near the body-drain junction preserves other device characteristics.
• Epitaxial layer tuning: Varying doping concentration in the epi-layer can create built-in electric fields that sweep out carriers during reverse recovery.

Thermal Management

The body diode's power dissipation (P_diss) during conduction is:

where I_F is forward current and R_on is the channel resistance. To minimize thermal resistance:

• Place source contacts uniformly across the die to prevent current crowding.
• Use thick top metal layers (≥4μm) for better heat spreading.
• Implement thermal vias under source pads to conduct heat to the package.

Advanced Layout Techniques

Trench MOSFET designs introduce additional considerations:

• Gate trench placement affects the body diode's current path - alternating trench and source stripes can improve performance.
• Superjunction structures require careful balancing of p and n pillar doping to maintain low V_F while achieving fast recovery.

In multi-die paralleled configurations, ensure symmetric layout to current sharing. Even small mismatches in bond wire lengths or die placement can cause significant current imbalance during diode conduction.

5.1 Curve Tracer Characterization

The intrinsic body diode of a MOSFET exhibits nonlinear conduction characteristics that can be precisely analyzed using a curve tracer. This instrument applies a swept voltage while measuring current, generating an I-V curve that reveals critical parameters such as forward voltage drop (V_F), reverse recovery charge (Q_rr), and dynamic resistance.

Measurement Setup and Methodology

A semiconductor curve tracer configures the MOSFET with drain and source terminals connected to the instrument's forcing and sensing leads, while the gate is held at zero potential to ensure the channel remains inactive. The voltage sweep typically ranges from -30 V to +3 V to capture both reverse-blocking and forward-conduction regimes. Key considerations include:

• Thermal stabilization: Maintain junction temperature at 25°C ±1°C using a thermal chuck to avoid parameter drift.
• Current compliance: Limit current to 1-10 A depending on package limits to prevent self-heating artifacts.
• Sweep rate: Use 100 ms/div or slower to allow steady-state conditions at each measurement point.

Characteristic Curve Interpretation

The resulting I-V plot reveals three distinct operational regions:

1. Reverse bias: Leakage current follows Shockley-Read-Hall generation until avalanche breakdown (V_BR).
2. Forward threshold: Current becomes measurable above the built-in potential (typically 0.7-1.2 V for silicon).
3. Ohmic region: Series resistance dominates at high currents, causing linear I-V slope.

Extracting Key Parameters

From the curve tracer data, calculate:

Modern curve tracers automate these calculations using numerical integration of the I(t) waveform during polarity reversal. For power MOSFETs, the reverse recovery time (t_rr) is typically measured between 90% I_RM points during diode turn-off.

Practical Considerations

When characterizing high-voltage MOSFETs (>600 V), the curve tracer must:

• Incorporate a snubber circuit to suppress ringing during reverse recovery.
• Use Kelvin connections to eliminate lead resistance errors.
• Implement guarded measurements for leakage currents below 1 μA.

Comparative studies show that body diode performance degrades with increased switching cycles due to stacking fault generation in the crystal lattice. This manifests as a 10-15% increase in V_F after 10⁶ switching events at rated current.

5.1 Curve Tracer Characterization

The intrinsic body diode of a MOSFET exhibits nonlinear conduction characteristics that can be precisely analyzed using a curve tracer. This instrument applies a swept voltage while measuring current, generating an I-V curve that reveals critical parameters such as forward voltage drop (V_F), reverse recovery charge (Q_rr), and dynamic resistance.

Measurement Setup and Methodology

A semiconductor curve tracer configures the MOSFET with drain and source terminals connected to the instrument's forcing and sensing leads, while the gate is held at zero potential to ensure the channel remains inactive. The voltage sweep typically ranges from -30 V to +3 V to capture both reverse-blocking and forward-conduction regimes. Key considerations include:

• Thermal stabilization: Maintain junction temperature at 25°C ±1°C using a thermal chuck to avoid parameter drift.
• Current compliance: Limit current to 1-10 A depending on package limits to prevent self-heating artifacts.
• Sweep rate: Use 100 ms/div or slower to allow steady-state conditions at each measurement point.

Characteristic Curve Interpretation

The resulting I-V plot reveals three distinct operational regions:

1. Reverse bias: Leakage current follows Shockley-Read-Hall generation until avalanche breakdown (V_BR).
2. Forward threshold: Current becomes measurable above the built-in potential (typically 0.7-1.2 V for silicon).
3. Ohmic region: Series resistance dominates at high currents, causing linear I-V slope.

Extracting Key Parameters

From the curve tracer data, calculate:

Modern curve tracers automate these calculations using numerical integration of the I(t) waveform during polarity reversal. For power MOSFETs, the reverse recovery time (t_rr) is typically measured between 90% I_RM points during diode turn-off.

Practical Considerations

When characterizing high-voltage MOSFETs (>600 V), the curve tracer must:

• Incorporate a snubber circuit to suppress ringing during reverse recovery.
• Use Kelvin connections to eliminate lead resistance errors.
• Implement guarded measurements for leakage currents below 1 μA.

Comparative studies show that body diode performance degrades with increased switching cycles due to stacking fault generation in the crystal lattice. This manifests as a 10-15% increase in V_F after 10⁶ switching events at rated current.

5.2 Dynamic Switching Tests

Dynamic switching tests characterize the transient behavior of the MOSFET body diode during high-frequency operation, where reverse recovery and capacitive effects dominate. Unlike static DC measurements, these tests reveal critical parameters such as reverse recovery time (t_rr), recovery charge (Q_rr), and switching losses.

Reverse Recovery Characteristics

When a MOSFET switches off, the body diode conducts until minority carriers recombine. The reverse recovery current (I_rr) is governed by the diode's stored charge and the rate of change of the applied voltage (dV/dt). The recovery time (t_rr) is derived from the carrier lifetime (τ) and doping concentration:

where I_F is the forward current before switching and I_R is the reverse current peak. The recovery charge Q_rr is the integral of the reverse current over t_rr:

Switching Losses and Diode Capacitance

Dynamic losses arise from the body diode's junction capacitance (C_j) and reverse recovery. The total switching energy loss (E_sw) per cycle combines conduction and recovery losses:

In high-frequency applications (e.g., DC-DC converters), E_sw scales linearly with frequency, making Q_rr a critical figure of merit.

Test Methodology

Industry-standard double-pulse testing isolates body diode behavior:

• Setup: A clamped inductive load forces current through the diode during MOSFET turn-off.
• Measurement: An oscilloscope captures V_DS, I_D, and I_rr to extract t_rr and Q_rr.
• Parameters: Test conditions (e.g., di/dt, temperature) must match operational limits.

Practical Implications

Fast-recovery diodes (e.g., SiC Schottky) minimize Q_rr but introduce trade-offs in forward voltage (V_F). Designers must balance:

• Efficiency: Lower Q_rr reduces losses but may increase conduction losses.
• EMI: Rapid di/dt during recovery generates high-frequency noise.
• Thermal Stress: Repeated high-energy recovery cycles degrade reliability.

5.2 Dynamic Switching Tests

Dynamic switching tests characterize the transient behavior of the MOSFET body diode during high-frequency operation, where reverse recovery and capacitive effects dominate. Unlike static DC measurements, these tests reveal critical parameters such as reverse recovery time (t_rr), recovery charge (Q_rr), and switching losses.

Reverse Recovery Characteristics

When a MOSFET switches off, the body diode conducts until minority carriers recombine. The reverse recovery current (I_rr) is governed by the diode's stored charge and the rate of change of the applied voltage (dV/dt). The recovery time (t_rr) is derived from the carrier lifetime (τ) and doping concentration:

where I_F is the forward current before switching and I_R is the reverse current peak. The recovery charge Q_rr is the integral of the reverse current over t_rr:

Switching Losses and Diode Capacitance

Dynamic losses arise from the body diode's junction capacitance (C_j) and reverse recovery. The total switching energy loss (E_sw) per cycle combines conduction and recovery losses:

In high-frequency applications (e.g., DC-DC converters), E_sw scales linearly with frequency, making Q_rr a critical figure of merit.

Test Methodology

Industry-standard double-pulse testing isolates body diode behavior:

• Setup: A clamped inductive load forces current through the diode during MOSFET turn-off.
• Measurement: An oscilloscope captures V_DS, I_D, and I_rr to extract t_rr and Q_rr.
• Parameters: Test conditions (e.g., di/dt, temperature) must match operational limits.

Practical Implications

Fast-recovery diodes (e.g., SiC Schottky) minimize Q_rr but introduce trade-offs in forward voltage (V_F). Designers must balance:

• Efficiency: Lower Q_rr reduces losses but may increase conduction losses.
• EMI: Rapid di/dt during recovery generates high-frequency noise.
• Thermal Stress: Repeated high-energy recovery cycles degrade reliability.

5.3 Thermal Imaging Methods

Thermal imaging provides critical insights into the behavior of the MOSFET body diode by mapping temperature distribution under operational stress. When the body diode conducts during reverse recovery or hard switching, localized heating occurs due to power dissipation (P_diss = I_FV_F). Infrared (IR) cameras and lock-in thermography are the primary techniques for capturing these thermal dynamics.

Infrared Thermography Principles

IR cameras detect emitted radiation in the 3–14 µm wavelength range, converting it into a temperature map. The Stefan-Boltzmann law governs the relationship between radiated power and temperature:

where ϵ is emissivity (0.9–0.95 for silicon), σ is the Stefan-Boltzmann constant (5.67×10⁻⁸ W/m²K⁴), and A is the emitting area. Emissivity calibration is essential to avoid errors from surface oxidation or packaging materials.

Lock-in Thermography for High Resolution

Periodic current excitation (typically 1–100 Hz) synchronizes with the IR camera’s sampling rate, isolating the thermal signature of the body diode from ambient noise. The phase-sensitive detection extracts the amplitude (ΔT) and phase lag (ϕ) of the thermal wave:

where μ is the thermal diffusion length (μ = √(α/πf)), and α is thermal diffusivity (8.8×10⁻⁵ m²/s for silicon). This method resolves sub-micron hotspots caused by non-uniform diode turn-off.

Practical Implementation

• Equipment: Mid-wave IR cameras (InSb detectors) with 20 mK thermal sensitivity.
• Sample Preparation: Remove heatsinks and apply high-emissivity coatings (e.g., black tape) to reduce reflections.
• Excitation: Pulse the MOSFET with I_F > rated current to accentuate body diode losses.

Case Study: Thermal Runaway Detection

A 100 V MOSFET in synchronous buck operation exhibited unexpected failure at 50 A load. Lock-in thermography revealed a 15°C hotspot at the body diode during dead-time conduction, traced to a localized defect in the epitaxial layer. The thermal resistance (R_θJA) was 40% higher than datasheet specifications due to voids in the die attach.

where T_j is junction temperature and T_a is ambient temperature. Corrective actions included optimizing the gate drive timing to minimize body diode conduction.

6.1 Key Research Papers

• PDF Chapter 6 — (5) Characteristics of p-n junction diode In the SPICE model of a MOSFET, the body-source and body-drain p-n junctions are modeled as p-n diodes [6.12]. The characteristics of the p-n junction diodes determine the transient body potential of a floating-body PD-SOI MOSFET [6.10],[6.13]. A MOSFET with an H- or T-shaped gate (Fig.
• PDF MODULE 6:Metal Oxide Semiconductor Field Effect Transistor (MOSFET) — MOSFET G S D Body diode Fig. 6.3: Parasitic BJT in a MOSFET cell. n+ n+ n+ n-D Body spreading resistance Parasitic BJT S G p One interesting feature of the MOSFET cell is that the alternating n+ n- p n+ structure embeds a parasitic BJT (with its base and emitter shorted by the source metallization) into each MOSFET cell as shown in Fig 6.3.
• Power Electronics Revolutionized: A Comprehensive Analysis of Emerging ... — During the conduction of the body diode, if the MOSFET is turned on, the forward characteristic of the body diode can be virtually improved, and, thus, the conduction losses are reduced. Figure 4 shows the calculated converter efficiency for a 1200-V SiC MOSFET system versus that is based on an IGBT/SiC diode hybrid power module.
• Mitigating reverse recovery power losses in MOSFET switching cell using ... — Despite the fair conduction behaviour of the MOSFET built-in body diode, whether silicon-based (Si) or silicon carbide-based (SiC), it still has a major weak point, namely reverse recovery losses during turn-off (Saro et al., 1998).These reverse recovery losses, due to the bipolar nature of the body diode (Nayak et al., 2020), challenges the economic advantages of exclusively relying on body ...
• Power MOSFETs | SpringerLink — This is referred to as current flow through the body diode of the power MOSFET. The body diode current flows when the drain bias voltage exceeds approximately 0.7 V in magnitude in the negative direction as shown in Fig. 6.7. It is possible to induce larger drain current flow at low negative drain bias voltages by the application of a gate bias.
• Soft recovery diodes with snappy behavior | Request PDF - ResearchGate — In this paper, the impact of the dead time on the performance and stability of 1.2 kV SiC MOSFET body diodes is characterised considering the variation of three factors (I) Gate turn-off voltage ...
• Considerations in the design of a low-voltage power MOSFET technology — When used as a synchronous rectifier, the body diode of the MOSFET conducts and contributes to power loss due to its forward voltage, V f, and stored charge. Fortunately, in a low-voltage MOSFET, the drift region is thin and highly doped with reductions in stored charge also aided by the body effect [47-49].
• Modelling and optimization of SiC MOSFET switching voltage and current ... — This paper considers the SiC MOSFET as fully on when the external drain-source voltage falls below 10% of its maximum value. The instant Q L turns fully on is denoted by t 4 as shown in Figure 2. Stage III starts from t 2 and ends at t 4. With the latest 3rd-generation technology, SiC MOSFET body diode recovers very fast with low reverse ...
• Analysis of the reverse recovery oscillation of superjunction MOSFET ... — For superjunction MOSFET body diode, due to the two dimensional depletion behavior, a long storage time t s is needed to build the charge balancing between the n-type and p-type columns. On the other hand, since the storage charge in the drift region is greatly removed by the two dimensional depletion in the end of phase 3, only small amount of ...
• (PDF) A survey of SiC power MOSFETs short-circuit robustness and ... — In such cases the device cannot be turned on anymore, but it is not entirely destroyed and preserves drainblocking capability. 3.2 Thermal Runaway Failure Drain Fig. 8. SiC MOSFET cell structure cross-sectional area during thermal runaway, including body diode and parasitic BJT. ICH: channel SC current; Ileak: drain leakage current.

6.2 Industry Application Notes

• PDF Designing with power MOSFETs - Infineon Technologies — The body diode is intrinsic to the MOSFET structure, formed by the p-n junction between p-body and n-epi layers shown in Figure 4. Power MOSFETs are three-terminal devices where the body and source are connected internally.1 This can be understood by looking at the circuit symbols for n- and P-channel devices.
• Power MOSFET Application Note - Renesas Electronics Corporation — The body diode may be used as a free wheel diode for regenerative current flow to the inverter circuit for motor control. When utilizing it in this manner and reverse voltage is applied immediately after the regenerative current, the MOSFET may be damaged depending on the circuit and operating conditions.
• PDF Half bridge resonant LLC converters and primary side MOSFET selection — The MOSFET is turned OFF while the current is circulating through the body diode and, since the antagonist MOSFET is turning ON, a body diode recovery can occur [4].
• PDF High-Voltage MOSFET Behavior in Soft-Switching Converters: Analysis and ... — The MOSFET is capable of very fast commutations and its intrinsic body diode saves an additional external component that would otherwise be necessary to clamp the switch voltage to the input supply voltage. Both the internal body diode and the output capacitance become essential components for the resonant transition.
• PDF The Power MOSFET Application Handbook Nexperia - Mouser Electronics — connections and general layout of the device. Note that the symbol is for an enhancement n-channel MOSFET with the source and body tied together, and a parallel diode between the source and drain. The parallel diode is known as t
• PDF 600 V CoolMOSTM CFD7 - Infineon Technologies — Scope and purpose The new 600 V CoolMOSTM CFD7 is Infineon's latest high voltage (HV) SJ MOSFET technology with integrated fast body diode. It completes the CoolMOSTM 7 series, addressing the high-power SMPS market. This new technology offers the lowest reverse recovery charge (Qrr) per on-state resistance (RDS(on)) on the market. This technical parameter gives new meaning to the word ...
• PDF MODULE 6:Metal Oxide Semiconductor Field Effect Transistor (MOSFET) — The reliance of the power electronics industry upon bipolar devices was challenged by the introduction of a new MOS gate controlled power device technology in the 1980s. The power MOS field effect transistor (MOSFET) evolved from the MOS integrated circuit technology. The new device promised extremely low input power levels and no inherent limitation to the switching speed. Thus, it opened up ...
• PDF AN-1001 - services.taiwansemi.com — Introduction When choosing a MOSFET, parameters that are focused on by most engineers intuitively are VDS, RDS(on), ID. However, in power systems, it is significant to pick up a suitable MOSFET based on different applications. In this application note, Taiwan Semiconductor (TSC) introduces the definition of every single parameter of a MOSFET, and from chapter 3, TSC also explains how each ...
• PDF Power MOS FET Application Note - u.dianyuan.com — In motor drive (power steering, starter generators, etc. in the case of electrical equipment) and switching power supply synchronous rectification applications that make positive use of a power MOSFET internal diode, there is a requirement for this reverse recovery time trr to be fast.

6.3 Advanced Textbook Chapters

• Uh Ece 6347 - Chapter 6 the Mos Field Effect Transistor (Mosfet) — 1 6. THE MOS FIELD EFFECT TRANSISTOR (MOSFET) We begin study of the MOSFET with the simpler MOS Gated Diode, a three terminal device. Like the capacitor, this device can be used for characterization, and in addition exhibits some important physics that will be used in discussion of the MOSFET. 6.1 THREE TERMINAL MOS (GATE-CONTROLLED DIODE) Modular Series: Advanced MOS, Figs. 2.8, 2.9 Geometry ...
• PDF Chapter 6 — The characteristics of the p-n junction diodes determine the transient body potential of a floating-body PD-SOI MOSFET [6.10],[6.13]. A MOSFET with an H- or T-shaped gate (Fig.
• PDF Advanced Power MOSFET Concepts - download.e-bookshelf.de — The body-diode can be used in place of the fly-back rectifier utilized in the H-bride circuit commonly used for motor control applications. It is demonstrated in this chapter that the judicious utilization of a Schottky contact within the power MOSFET cell structure can greatly improve the reverse recovery behavior of the body-diode.
• Advanced Power Mosfet Concepts [PDF] [6km7a0j7d6j0] — It is demonstrated in this chapter that the judicious utilization of a Schottky contact within the power MOSFET cell structure can greatly improve the reverse recovery behavior of the body-diode.
• PDF MODULE 6:Metal Oxide Semiconductor Field Effect Transistor (MOSFET) — The body diode of a MOSFET has the same break down voltage and forward current rating as the main MOSFET. The switching delays in a MOSFET are due to finite charging and discharging time of the input and output capacitors.
• PDF Chapter 6 MOSFET — Chapter 6 MOSFET The MOSFET (MOS Field-Effect Transistor) is the building block of Gb memory chips, GHz microprocessors, analog, and RF circuits.
• PDF Microsoft PowerPoint - Lect. 19 MOSFET [호환 모드] - Yonsei — (Razavi 6.2,6.3) MOSFET: Metal Oxide Semiconductor Field Effect Transistor Source Control current flow between S and D with voltage applied at G NMOS, PMOS
• PDF MOS Transistor - Chenming Hu — 6.4 MOSFET Vt, Body Effect, and Steep Retrograde Doping with bipolar transistors, which have forward-biased diodes at the input and draw significant input current (see Chapter 8).
• PDF MOSFET CHAPTER 6 - miun.se — As the channel length decreases, the depletion widths of the source and drain become comparable to the channel length and punch-through between the drain and source will eventually occur Even with best practice, keeping long-channel behavior becomes impossible short-channel effects cause 2-d potential distribution high channel electric field
• PDF Microsoft PowerPoint - ch06updated [Compatibility Mode] — The inversion channel of a MOSFET can be seen as a resistor. Since the charge density inside the channel depends on the gate voltage, this resistance is also voltage-dependent.