Definition and Basic Operation

A Zinc Oxide Varistor (ZnO varistor) is a highly nonlinear voltage-dependent resistor primarily used for transient voltage suppression in electrical circuits. Its operation is based on the unique electrical properties of sintered zinc oxide grains doped with small amounts of bismuth, cobalt, manganese, and other metal oxides. The microstructure consists of conductive ZnO grains separated by insulating grain boundaries, forming a polycrystalline network.

Nonlinear Current-Voltage Characteristics

The defining feature of a ZnO varistor is its highly nonlinear I-V relationship, which can be approximated by the empirical equation:

where:

• I is the current through the varistor,
• V is the applied voltage,
• k is a material-dependent constant,
• α is the nonlinearity coefficient (typically 30–100 for ZnO varistors).

At low voltages, the varistor behaves like an insulator, with minimal leakage current. When the voltage exceeds a threshold (breakdown voltage), the grain boundaries become conductive, allowing a sharp increase in current while clamping the voltage.

Microscopic Conduction Mechanism

The nonlinearity arises from the Schottky barriers at the grain boundaries. Under normal conditions, these barriers prevent current flow. When the electric field exceeds a critical value, electrons tunnel through the barriers via the Poole-Frenkel effect or thermionic emission. The breakdown voltage per grain boundary is typically 2–3 V, meaning the total clamping voltage scales with the number of grain boundaries in series.

Equivalent Circuit Model

A simplified equivalent circuit consists of:

• A nonlinear resistor representing the grain boundary barriers,
• A small intrinsic capacitance due to the depletion regions,
• A series resistance from the bulk ZnO grains.

where R_s is the series resistance, C is the capacitance, and R_nl(V) is the voltage-dependent nonlinear resistance.

Practical Applications

ZnO varistors are widely used in:

• Surge protection devices (SPDs) for power lines,
• Voltage clamping in electronic circuits,
• Transient suppression in automotive and industrial systems.

Their fast response time (nanoseconds) and high energy absorption capability make them ideal for protecting sensitive electronics from voltage spikes caused by lightning strikes, inductive load switching, or electrostatic discharge (ESD).

Key Electrical Characteristics

Nonlinear Voltage-Current Relationship

The defining characteristic of a ZnO varistor is its highly nonlinear voltage-current (V-I) relationship, governed by the following empirical equation:

where I is the current, V is the voltage, k is a material-dependent constant, and α is the nonlinearity coefficient. For ZnO varistors, α typically ranges from 20 to 100, significantly higher than traditional silicon carbide varistors (α ≈ 3–7). The high α value ensures sharp clamping behavior during transient events.

Clamping Voltage and Energy Absorption

The clamping voltage (V_C) is the voltage at which the varistor begins conducting significant current (usually defined at 1 mA). This parameter is critical for surge protection applications, as it determines the maximum voltage let-through during a transient event. The energy absorption capability (W) is given by:

where the integration is performed over the duration of the transient. ZnO varistors can absorb energy densities up to 300 J/cm³, making them suitable for high-energy surge suppression.

Leakage Current and Degradation

Below the clamping voltage, ZnO varistors exhibit a small leakage current (typically <1 μA). However, repeated exposure to surges causes grain boundary degradation, increasing leakage current over time. This aging effect is modeled by:

where I₀ is the initial leakage current, β is the degradation rate, and t is time. Excessive leakage current can lead to thermal runaway, necessitating periodic monitoring in critical applications.

Capacitance and Frequency Response

Due to their polycrystalline structure, ZnO varistors exhibit inherent capacitance (C), typically in the range of 100 pF to 10 nF. The capacitance decreases with increasing voltage, following:

where C₀ is the zero-bias capacitance, V₀ is a reference voltage, and γ is an empirical constant. This voltage-dependent capacitance limits high-frequency performance, making ZnO varistors less suitable for RF applications.

Response Time and Pulse Handling

ZnO varistors respond to transients in nanoseconds, but the actual clamping performance depends on the parasitic inductance of the package and leads. For standard disk varistors, the effective response time is typically <25 ns. The pulse current rating (I_PP) is specified for standard waveforms like 8/20 μs (rise/fall time) and 10/1000 μs, with commercial devices handling peak currents up to 100 kA.

1.3 Material Composition and Structure

Crystalline Structure of ZnO Varistors

The nonlinear electrical behavior of zinc oxide (ZnO) varistors arises from their polycrystalline microstructure, primarily composed of ZnO grains doped with small amounts of bismuth oxide (Bi₂O₃), antimony oxide (Sb₂O₃), cobalt oxide (CoO), and manganese oxide (MnO). The ZnO grains, typically 5–50 μm in diameter, exhibit n-type semiconductor properties with a wurtzite crystal structure (hexagonal, space group P6₃mc). These grains are separated by thin intergranular layers (~0.1–1 μm thick) rich in Bi₂O₃, forming a three-dimensional network of double Schottky barriers at grain boundaries.

Role of Dopants in Electrical Properties

The addition of Bi₂O₃ promotes liquid-phase sintering at temperatures around 1100–1200°C, facilitating the formation of insulating grain boundary phases. Sb₂O₃ inhibits ZnO grain growth during sintering, while CoO and MnO modify the trap states at grain boundaries, enhancing nonlinearity. The resulting voltage-current characteristic follows:

where α (nonlinear coefficient) typically ranges from 30–70, and k is a material constant. The breakdown voltage V_b per grain boundary is approximately 3–4 V, making the overall varistor voltage dependent on the number of grain boundaries along the current path.

Microstructural Analysis Techniques

Advanced characterization methods reveal critical details:

• Scanning Electron Microscopy (SEM): Visualizes grain size distribution and porosity
• Energy-Dispersive X-ray Spectroscopy (EDS): Maps elemental segregation at grain boundaries
• Impedance Spectroscopy: Quantifies grain and grain boundary resistances

Thermodynamic Considerations

The defect chemistry of ZnO varistors is governed by oxygen adsorption at grain boundaries, creating acceptor states. The equilibrium oxygen partial pressure P_O2 during sintering affects oxygen vacancy concentration:

This relationship directly influences the barrier height φ_b at grain boundaries, typically 0.7–1.2 eV, which determines the varistor's clamping voltage.

Industrial Manufacturing Processes

Commercial production involves:

• Ball milling of raw powders (99.99% purity) for homogeneous mixing
• Uniaxial or isostatic pressing at 50–200 MPa
• Sintering in controlled atmosphere furnaces
• Electrode application (typically silver or aluminum)

The resulting microstructure exhibits a breakdown field strength of 200–500 V/mm, with energy absorption capacity reaching 300 J/cm³ in high-performance formulations.

2.1 Nonlinear Voltage-Current Behavior

The defining characteristic of zinc oxide varistors (ZnO varistors) is their highly nonlinear voltage-current (V-I) relationship, which enables them to act as voltage-dependent resistors. Below the breakdown voltage, the device exhibits high resistance, allowing only minimal leakage current. Once the applied voltage exceeds the threshold, the resistance drops sharply, diverting surge currents away from sensitive components.

Mathematical Modeling of the V-I Curve

The nonlinear behavior is empirically described by the power-law relation:

where:

• I is the current through the varistor,
• V is the applied voltage,
• k is a material-dependent constant,
• α is the nonlinearity coefficient (typically between 20 and 100 for ZnO varistors).

For a more precise representation in the pre-breakdown region, the V-I relationship can be expanded to include the leakage current component:

Here, I₀ and V₀ characterize the ohmic leakage at low voltages.

Physical Mechanism Behind Nonlinearity

The nonlinearity arises from the grain-boundary barriers in the polycrystalline ZnO structure. Each grain boundary forms a double Schottky barrier, which blocks current flow at low voltages. When the electric field exceeds a critical value, electrons tunnel through the barriers via the Poole-Frenkel effect, leading to the sharp increase in conductivity.

Practical Implications in Circuit Protection

The steep V-I curve allows ZnO varistors to:

• Clamp transient overvoltages within nanoseconds,
• Dissipate high surge energies (up to several kJ) without degradation,
• Self-reset after the surge subsides, unlike fuses or crowbar devices.

In power systems, this behavior protects against lightning strikes and switching transients, while in electronics, it safeguards sensitive ICs from electrostatic discharge (ESD).

Temperature Dependence and Aging Effects

The V-I characteristics shift with temperature due to changes in the barrier height φ_B:

where k is Boltzmann's constant and T is absolute temperature. Repeated surges can cause gradual barrier degradation, increasing leakage current over time—a critical factor in reliability assessments.

2.2 Transient Voltage Suppression Mechanism

The transient voltage suppression mechanism in zinc oxide (ZnO) varistors arises from their highly nonlinear current-voltage (I-V) characteristics, governed by the formation of double Schottky barriers at grain boundaries. When subjected to a transient overvoltage, the varistor transitions from a high-resistive state to a highly conductive state, clamping the voltage to a safe level.

Nonlinear Electrical Behavior

The I-V relationship of a ZnO varistor is empirically described by:

where I is the current, V is the voltage, k is a material-dependent constant, and α is the nonlinear coefficient, typically ranging from 30 to 100 for commercial varistors. The higher α, the sharper the transition from insulating to conducting behavior.

Double Schottky Barrier Model

The nonlinearity originates from the potential barriers formed at the grain boundaries between ZnO grains. Under normal operating conditions, these barriers inhibit current flow. When the applied voltage exceeds the breakdown threshold (V_b), electrons tunnel through the barrier via the Poole-Frenkel effect or thermionic emission, drastically reducing resistance.

where J is the current density, J₀ is the saturation current density, φ_B is the barrier height, E is the electric field, β is the field-lowering coefficient, k is Boltzmann’s constant, and T is the temperature.

Transient Energy Absorption

During a transient event, the varistor absorbs energy (E) given by:

The energy-handling capability is determined by the heat dissipation rate and thermal mass of the varistor. Excessive energy leads to thermal runaway, causing permanent degradation.

Practical Considerations

• Response Time: ZnO varistors respond to transients in nanoseconds, making them suitable for fast-rising surges like lightning strikes.
• Clamping Voltage: The varistor maintains the voltage near V_b during conduction, protecting downstream components.
• Degradation Mechanisms: Repeated surges or overstress can cause barrier deterioration, increasing leakage current.

Applications in Circuit Protection

ZnO varistors are widely used in:

• Power supply input stages to suppress line surges.
• Telecommunication circuits for lightning protection.
• Industrial equipment to mitigate switching transients.

2.3 Common Applications in Circuit Protection

Zinc oxide varistors (ZnO varistors) are widely employed in circuit protection due to their highly nonlinear voltage-current characteristics and fast response to transient overvoltages. Their primary function is to clamp voltage spikes by transitioning from a high-resistance state to a low-resistance state when the threshold voltage is exceeded. This behavior makes them indispensable in several critical applications.

Power Supply Protection

ZnO varistors are commonly integrated into AC and DC power supplies to suppress voltage transients induced by lightning strikes, inductive load switching, or electrostatic discharge (ESD). In AC power lines, they are typically connected between line and neutral, while in DC systems, they are placed across the supply rails. Their energy absorption capability, quantified by the joule rating, determines their suitability for different power levels. The energy dissipated during a transient event can be approximated by:

where V(t) and I(t) are the time-dependent voltage and current during the clamping action.

Telecommunications Equipment

In telecommunication systems, ZnO varistors protect sensitive circuitry from surges caused by lightning-induced coupling or power cross faults. They are often used in conjunction with gas discharge tubes (GDTs) and transient voltage suppression (TVS) diodes to form a multi-stage protection scheme. The varistor's low capacitance (< 100 pF) minimizes signal distortion, making it suitable for high-frequency applications.

Industrial Motor Drives

Variable frequency drives (VFDs) and servo controllers incorporate ZnO varistors to mitigate voltage spikes generated by inductive kickback from motor windings. The repetitive nature of these transients requires varistors with high energy endurance and minimal degradation over time. The lifetime expectancy can be modeled using the Arrhenius equation:

where L is the operational lifetime, A is a material constant, E_a is the activation energy, k is Boltzmann's constant, and T is the absolute temperature.

Consumer Electronics

Modern consumer devices leverage ZnO varistors for IEC 61000-4-5 compliance, particularly in power adapters, USB ports, and HDMI interfaces. Their compact form factor (often in surface-mount packages) allows integration into space-constrained designs while providing robust protection against ESD events up to 8 kV.

Automotive Systems

Automotive 12V/24V systems employ ZnO varistors to protect electronic control units (ECUs) from load dump transients (ISO 7637-2) and alternator field decay surges. The varistors in these applications must withstand extreme temperature ranges (-40°C to +125°C) while maintaining stable clamping characteristics.

High-Voltage Transmission Systems

In utility-scale applications, stacked ZnO varistor columns form the core of surge arresters for transmission lines and substations. These assemblies must handle impulse currents exceeding 100 kA while maintaining thermal stability. The voltage gradient across the column is given by:

where n is the number of varistor discs in series and d is the thickness of each disc.

3.1 Voltage Ratings and Clamping Voltage

The nonlinear current-voltage (I-V) characteristics of zinc oxide varistors (ZnO) are governed by their voltage ratings and clamping behavior. The varistor voltage (V_N) is defined as the voltage across the device at a specified DC current (typically 1 mA), while the clamping voltage (V_C) represents the peak voltage during transient suppression.

Varistor Voltage (V_N)

The varistor voltage is derived from the empirical relation:

where C is a material-dependent constant, I is the current, and β is the nonlinear coefficient (typically 20–50 for ZnO varistors). For a standard 20 mm disk varistor, V_N at 1 mA ranges from 18 V to 820 V, depending on the formulation.

Clamping Voltage (V_C)

Under high-current transients (e.g., 8/20 μs surge), the clamping voltage follows:

where K is a device-specific constant, I_p is the peak surge current, and α (0.02–0.06) describes the weak current dependence. For example, a 275 V_RMS varistor may clamp a 100 A surge to ~450 V.

Voltage Ratio and Energy Absorption

The voltage ratio (V_C/V_N) quantifies clamping efficiency, with lower values (1.5–2.5) indicating better performance. Energy absorption is given by:

where the integral spans the transient duration. High-energy varistors achieve >300 J/cm³ by optimizing grain boundary barriers.

Practical Design Considerations

• Derating: Operating voltage should be ≤50% of V_N to avoid degradation.
• Temperature Effects: V_N decreases by ~0.1%/°C; thermal runaway occurs above 150°C.
• Pulse Life: Clamping capability degrades after 10²–10⁴ surges, depending on I_p.

3.2 Energy Absorption Capacity

The energy absorption capacity of a zinc oxide (ZnO) varistor is a critical parameter defining its ability to dissipate transient overvoltage events without degradation. This capacity is determined by the volumetric energy density of the ZnO microstructure and the thermal dissipation characteristics of the device.

Mathematical Derivation of Energy Handling

The total energy E absorbed during a transient event is given by the time integral of the instantaneous power dissipation:

For practical engineering purposes, this is often approximated using the peak surge current I_p and clamping voltage V_c over the pulse duration Δt:

The energy density E_v per unit volume relates to the microscopic breakdown characteristics of the ZnO grains:

where E_bd is the breakdown field strength (typically 3-4 kV/mm in ZnO varistors), ε₀ is the vacuum permittivity, and ε_r is the relative permittivity of ZnO (≈1000).

Thermal Considerations and Practical Limits

The maximum energy absorption is ultimately constrained by thermal runaway effects. The adiabatic temperature rise ΔT can be estimated as:

where m is the mass of the active ZnO material and c_p is its specific heat capacity (≈500 J/kg·K). Exceeding 150-200°C typically leads to degradation of the grain boundary barriers.

Manufacturing and Design Factors

Key parameters affecting energy absorption include:

• Varistor disk diameter: Larger diameters provide greater thermal mass and current handling
• Grain size distribution: Uniform 5-10 μm grains optimize breakdown characteristics
• Additive composition: Bi₂O₃, Sb₂O₃, and other dopants control grain boundary properties
• Electrode design: Thermal coupling to heatsinks extends energy limits

Standard Test Methods

IEC 61000-4-5 defines standardized surge waveforms for testing:

• 8/20 μs current wave (lightning surge simulation)
• 10/350 μs current wave (direct strike)
• 1.2/50 μs voltage wave

Manufacturers typically specify energy ratings for:

• Single pulse maximum (e.g., 300 J for a 20mm disk)
• Repetitive pulse capability (e.g., 50 J per pulse at 1 pulse/minute)

Response Time and Durability

Response Time Characteristics

The response time of a zinc oxide varistor (ZnO) is a critical parameter in transient voltage suppression applications. Unlike traditional silicon-based devices, ZnO varistors exhibit an exceptionally fast response, typically in the nanosecond range (1–5 ns). This rapid reaction is due to the polycrystalline structure of ZnO grains separated by insulating barriers, which undergo avalanche breakdown under high electric fields.

The response time t_r can be derived from the varistor's intrinsic capacitance C and dynamic resistance R_d during conduction:

where R_d is the dynamic resistance in the conducting state, typically in the milliohm range, and C is the junction capacitance, which depends on the varistor's physical dimensions and grain boundary properties.

Durability and Degradation Mechanisms

ZnO varistors are subject to gradual degradation under repeated transient stresses. The primary failure modes include:

• Thermal runaway due to excessive energy absorption leading to localized heating.
• Grain boundary deterioration caused by high-current impulses, reducing the nonlinear coefficient α.
• Oxidation of electrode contacts under prolonged exposure to high humidity.

The lifetime L of a varistor under repetitive surge conditions follows an empirical power-law relationship:

where L₀ is the reference lifetime at energy stress E₀, E is the applied energy per surge, and n is an exponent typically between 5–10 for commercial ZnO varistors.

Practical Implications for Circuit Design

For high-reliability applications, engineers must consider:

• Derating – Operating the varistor below its maximum rated energy and voltage.
• Thermal management – Ensuring adequate heat dissipation to prevent thermal stress accumulation.
• Pulse endurance testing – Validating performance under standardized surge conditions (e.g., IEEE C62.41).

Advanced formulations, such as bismuth- or praseodymium-doped ZnO, improve durability by enhancing grain boundary stability. These materials exhibit superior resistance to degradation under high-current impulses, making them suitable for industrial power systems.

Case Study: Surge Protection in Power Grids

In high-voltage transmission systems, ZnO varistors are subjected to lightning-induced surges. Field studies show that properly rated varistors withstand 10⁴–10⁶ surge events before significant parameter drift occurs. However, performance varies with:

• Waveform characteristics (8/20 μs vs. 10/350 μs).
• Ambient temperature (higher temperatures accelerate aging).
• Clamping voltage stability over operational lifetime.

4.1 Benefits Over Other Surge Protection Devices

Nonlinear Voltage-Current Characteristics

Zinc oxide varistors (ZnO) exhibit highly nonlinear voltage-current behavior, governed by the empirical relation:

where k is a material-dependent constant and α typically ranges between 30–100. This sharply contrasts with silicon avalanche diodes (α ≈ 5–20) and gas discharge tubes (α ≈ 10–30), enabling ZnO varistors to clamp voltages more effectively during fast transients. The nonlinearity arises from grain-boundary effects in the polycrystalline ZnO matrix, where Schottky barriers form between conductive ZnO grains and insulating intergranular layers.

Energy Absorption Capacity

ZnO varistors outperform competing technologies in energy handling per unit volume. A standard 20mm disk can absorb 300–500 J/cm³, compared to 5–50 J/cm³ for TVS diodes and 100–200 J/cm³ for spark gaps. This stems from:

• Bulk conduction: Current distributes across the entire volume rather than being confined to junctions
• Thermal stability: The negative temperature coefficient of resistance above threshold voltage promotes self-healing
• Microstructural design: Controlled doping (Bi₂O₃, Sb₂O₃) optimizes grain boundary properties

Response Time and Frequency Characteristics

The intrinsic response time of ZnO varistors is sub-nanosecond, limited only by capacitive effects (typically 100–500 pF for a 20mm disk). This makes them effective against ESD (rise time ~1 ns) and lightning-induced surges (8/20 μs waveform). In contrast:

Degradation Mechanisms and Lifetime

Unlike silicon devices that fail catastrophically, ZnO varistors exhibit gradual degradation. The primary mechanisms include:

where E_a is activation energy (~0.8–1.2 eV) and J is current density. Progressive grain boundary deterioration increases leakage current but maintains surge protection capability. Accelerated aging tests at 85°C/85% RH show 10⁴–10⁶ surge cycles before 10% parameter shift, compared to 10²â€“10³ cycles for polymer-based devices.

System-Level Advantages

In three-phase power systems (e.g., 480V AC industrial lines), ZnO varistors provide:

• Voltage gradient matching: Parallel/series stacks maintain uniform voltage distribution without balancing circuits
• Fault tolerance: Single-element failure doesn't compromise entire protection system
• DC stability: No polarity dependence unlike semiconductor devices

4.2 Thermal and Aging Considerations

Thermal Runaway and Power Dissipation

Zinc oxide varistors (ZnO) exhibit nonlinear voltage-current characteristics, but under sustained overvoltage conditions, Joule heating dominates. The power dissipation P in a varistor is given by:

where I₀ and V₀ are reference current and voltage, and α is the nonlinear coefficient (typically 30–100). Thermal runaway occurs when heat generation exceeds dissipation, governed by:

Here, k is the thermal conductance, C_th is the thermal capacitance, and T_amb is ambient temperature. Exceeding the critical temperature (T_crit ≈ 150–200°C) degrades the grain-boundary barriers irreversibly.

Aging Mechanisms

Long-term degradation arises from:

• Electromigration: Ion migration under high electric fields alters grain-boundary potentials.
• Oxidation: Oxygen diffusion at elevated temperatures increases leakage current.
• Thermal Cycling: Repeated expansion/contraction fractures intergranular contacts.

The aging rate follows an Arrhenius model:

where E_a is activation energy (~1.0–1.5 eV for ZnO) and Ï„₀ is a pre-exponential factor.

Practical Mitigation Strategies

To extend operational lifetime:

• Derating: Operate at ≤75% of rated voltage to reduce I_leakage.
• Thermal Management: Use heatsinks or active cooling for high-energy applications.
• Material Engineering: Dopants (Bi₂O₃, Sb₂O₃) stabilize grain boundaries against ion migration.

Accelerated Aging Tests

Industry standards (IEC 60099-4) prescribe:

• High-Temperature Storage: 1000 hours at 85–125°C with periodic V_1mA measurements.
• Cyclic Loading: 10⁴ pulses at 8/20 μs waveform to simulate surge events.

Failure criteria include a >10% shift in V_1mA or leakage current doubling.

4.3 Environmental and Operational Constraints

Zinc oxide varistors (ZnO varistors) exhibit performance dependencies on environmental and operational conditions, which must be carefully considered in high-reliability applications. Key constraints include temperature effects, humidity exposure, mechanical stress, and long-term degradation mechanisms.

Temperature Dependence

The nonlinear current-voltage (I-V) characteristics of ZnO varistors are strongly influenced by temperature. The leakage current increases exponentially with temperature, governed by the Arrhenius relation:

where I_L is the leakage current, E_a is the activation energy, k is Boltzmann's constant, and T is the absolute temperature. At elevated temperatures, the varistor voltage V_1mA (voltage at 1 mA current) decreases by approximately 0.05–0.1% per °C.

Humidity and Contamination

ZnO varistors are susceptible to performance degradation in high-humidity environments due to electrochemical reactions at grain boundaries. Moisture ingress can lead to:

• Increased leakage current due to ionic conduction
• Reduced energy absorption capability
• Accelerated aging under DC bias

Hermetic sealing or conformal coatings are often employed in humid environments to mitigate these effects.

Mechanical Stress

Mechanical stresses—whether from thermal cycling, vibration, or improper mounting—can induce microcracks in the ceramic structure, compromising surge protection capability. The fracture toughness K_IC of ZnO varistor material is typically in the range of 1–2 MPa·m^1/2.

Long-Term Degradation

Under continuous AC or DC voltage stress, ZnO varistors experience gradual degradation characterized by:

where A is a material constant, Q is the activation energy for degradation, and n is the voltage acceleration factor (typically 2–4). This leads to a gradual decrease in varistor voltage and increased leakage current over time.

Frequency Effects

At high frequencies (>1 MHz), the capacitive component of the varistor impedance becomes significant. The complex impedance Z(ω) can be modeled as:

where R(ω) is the frequency-dependent resistive component and C(ω) is the geometric capacitance. This frequency dependence must be accounted for in high-speed surge protection applications.

Thermal Runaway

Under sustained overvoltage conditions, the power dissipation P = V²/R can lead to thermal runaway if the heat generation exceeds dissipation capability. The critical energy absorption limit W is given by:

where t_f is the time to failure. Exceeding this limit results in catastrophic failure through thermal cracking or melting of electrodes.

5.1 Key Research Papers and Patents

• Zinc Oxide Materials for Electronic and Optoelectronic Device Applications — 1.3 Optical Properties 5 1.3.1 Free and Bound Excitons 5 1.3.2 Effects of External Magnetic Field on ZnO Excitons 6 1.3.3 Strain Field 8 1.3.4 Spatial Resonance Dispersion 9 1.4 Electrical Properties 10 1.4.1 Intrinsic Electronic Transport Properties 10 1.4.2 n-type Doping and Donor Levels 11 1.4.3 p-type Doping and Dopability 13
• PDF The Comprehensive Performance of ZnO Varistors Regulated by the ... — The Comprehensive Performance of ZnO Varistors Regulated by the Formulation System and Sintering Process Yue Yin 1, Pengfei Meng1(B),XiaoLei2, Chengxin Li2, Lei Wang3, Kui Miao4, Jingke Guo1, and Tengfei Li1 1 College of Electrical Engineering, Sichuan University, Chengdu 610065, China [email protected] 2 State Grid Sichuan Electric Power Research Institute, Chengdu 610041, China
• Electrical characteristics of SrCoO3-added zinc oxide varistors - J-STAGE — Fig. 2. Relationship between varistor voltage and inverse of grain size for SCO0.25­3. as a function of SCO content. Fig. 3. ¡ as and deg for SCO0.25­3. as a function of SCO content. JCS-Japan Kurokawa et al.: Electrical characteristics of SrCoO 3-added zinc oxide varistors 584
• PDF STABILITY OF ZINC OXIDE VARISTORS - Research Explorer The University of ... — Figure 5-1 Particle size of the base composition prepared by different techniques .....79 Figure 5-2 SEM images of dried powder after milling .....80 Figure 5-3 Densities of the AMBC and CMBC varistors as a function of sintering
• Effectively enhanced comprehensive electrical performance of ZnO ... — According to the previous research, the introduction of raw materials with fine particles could greatly improve the microstructure and the electrical properties of the varistors [[13], [14], [15], [16]].All kinds of additive materials should be refined in advance to ensure the uniform reaction between the additives and the main material-ZnO with an average particle size around 500 nm during ...
• IMPROVEMENT OF THE V-I CHARACTERISTIC OF ZINC OXIDE (ZnO) BASED METAL ... — IMPROVEMENT OF THE V-I CHARACTERISTIC OF ZINC OXIDE (ZnO) BASED METAL OXIDE VARISTORS (MOVs) USING SILICON TELLURIDE (SiTe2) AND LANTHANUM HEXABORIDE (LaB6) MATERIALS ... Jandrell, for his guidance in carrying out this research. It is through his vision and expertise that I got to this academic platform. I cherish his words of wisdom
• Improvements in the Electronic Performance of ZnO-Based Varistors by ... — Varistors processed from mixtures of certain metal oxides (as additives to the main component, zinc oxide, ZnO), called MOVs, represent the devices most used for overvoltage protection and are integrated into the construction of high-performance surge arresters. The manufacturing process of these powerful electronic devices is crucial for their electronic performance.
• Electrical characteristics of SrCoO3-added zinc oxide varistors — The electrical degradation of zinc oxide varistors (ZnO; Bi2O3 and CoO or Bi2O3 and MnO2) was evaluated by ICTS (Isothermal Capacitance Transient Spectroscopy) method from -180°C to 80°C to ...
• PDF Research on a high performance multilayer ZnO varistor and its ... — of electronic products, the demands for multilayer chip varistors (MLV) which are designed for surge protection and electrostatic discharge (ESD) protection in circuits are increasing rapidly and the requirements for the MLV's properties become stricter. In order to meet the demands of "green" production methods in an environmental
• (PDF) The role of oxide optimization in improving the electrical ... — The role of oxide optimization in improving the electrical properties of ZnO varistors November 2021 Journal of Materials Science: Materials in Electronics 32(24)

5.2 Industry Standards and Datasheets

• PDF PRODUCT Metal Oxide Varistor SERIES JVZ Series - PDC — Metal Oxide Varistor JVZ Series 2 Standard Series Specification Agency Approvals Agency UL cUL VDE CQC Agency Approvals UL1449 4th Edition CSA 22.2 No. 269.5-17 IEC61051-1 IEC61051-2 IEC61051-2-2 IEC61051-1 IEC61051-2 IEC61051-2-2 IEC62368-1:2018/G.8.1 GB/T10193-1997 GB/T10194-1997 GB4943.1-2011 GB/T10193-1997 GB/T10194-1997 GB8898-2011 Title
• PDF VDR Metal Oxide Varistors Standard - Vishay Intertechnology — VDR Metal Oxide Varistors Standard LINKS TO ADDITIONAL RESOURCES ORDERING INFORMATION ... •Low β high purity zinc oxide disc • Halogen free insulating epoxy coating • Straight leads and kinked leads ... 53 2.5 2.0 250 0.15 2000 4.1 0.8 ± 0.3 VDRS07B017xyE
• PDF MOV-20DxxxK Series - Metal Oxide Varistor - RS Components — MOV-20DxxxK Series - Metal Oxide Varistor *RoHS Directive 2002/95/EC Jan. 27, 2003 including annex and RoHS Recast 2011/65/EU June 8, 2011. Specifications are subject to change without notice. Customers should verify actual device performance in their specific applications. Industry Standard Compliance Standard UL 1449 File Number E313168
• PDF Zinc Oxide Varistors - Digi-Key — Zinc Oxide Varistors VE 07/09/13/17/24 VF 05/07/10/14/20 FEATURES • Radial lead varistors • Wide operating voltage range from 14 V to 625 V (V rms for VE types) or 22 V to 1000 V (V 1mA for VF types) • Available in tape and reel for use with automatic insertion equipment (see pages 31 to 33 for details). PARTICULAR CHARACTERISTICS E D t ...
• PDF Metal Oxide Varistors (MOV) Data Sheet - ElecFans — The maximum energy within the varistor voltage change of ±10% when one impulse of 10/1000μs or 2ms is applied. Withstanding Surge Current The maximum current within the varistor voltage change of ±10% with the standard impulse current (8/20μs) applied one time. Varistor Voltage Temp. Coefficient V 1mA@105℃-V 1mA@25℃ V 1mA@25℃ × 1 80 ...
• ERZ-E Series Varistors | Panasonic Industrial Devices — Panasonic's ERZ-E Series Radial Leaded Disc ZNR® Transient/Surge Absorbers feature large surge current and energy handling capability for absorbing transient overvoltage in compact sizes. ZNR stands for Zinc-oxide Non-linear Resistor, also commonly known as Metal Oxide Varistor or MOV. Panasonic invented the ZNR Surge Absorber in 1968 and is a pioneer in the use of Zinc Oxide as a Surge Absorber.
• PDF STANDARD SERIES - Midan Elec — Zinc Oxide Varistor 5. AC Voltage Rating Two significant figures plus number of zeroes that follow, i.e. 131 is 130 VAC 6. Special Instructions, RA is standard 7. Rating Code, up to four numbers The Standard Series is our broadest and most comprehensive line of radial-leaded varistors. These components consist of wire leads and have nominal
• PDF SIOV metal oxide varistors - TDK Electronics AG — is highly resistive. Only at those points where zinc oxide grains meet does sintering produce "microvaristors", comparable to symmetrical zener diodes (protection level approx. 3.5 V). The electrical behavior of the metal oxide varistor, as indicated by figure 3, results from the number of microvaristors connected in series or in parallel.
• PDF Metal Oxide Varistors (MOV) Data Sheet - YAGEO — Metal Oxide Varistors (MOV) Data Sheet Features Wide operating voltage (V 1mA) range from 18V to 1800V Fast responding to transient over-voltage Large absorbing transient energy capability Low clamping ratio and no follow-on current Meets MSL level 1, per J-STD-020 Operating Temperature：-40℃ ~ +105℃
• PDF The DatasheetArchive - Datasheet Search Engine - Ersin Elektronik — ZOV(Zinc Oxide Varistor) varistors are nonlinear two-electrode semiconductor voltage-dependant resistors, which are designed for transient voltage suppression and surge energy absorption. Transient over-voltages are a major cause for malfunction or total failure of electronic circuitry and equipment.

5.3 Recommended Books and Online Resources

• Zinc Oxide Varistor: Features | PDF | Physical Quantities - Scribd — zinc_oxide_varistor - Free download as PDF File (.pdf), Text File (.txt) or read online for free. Zinc oxide varistors are non-linear resistors composed mainly of zinc oxide that change resistance with applied voltage. They have a wide voltage range from 18V to 1.8kV and fast response time of 25ns. They can withstand high surge currents of up to 2000A/cm2 and have a long life.
• PDF Zinc Oxide Varistor - techno-star.biz — Zinc Oxide Varistor 1 SPECIFICATION TVR Series (Surge Protection) Features Recommended Applications Approvals 1. Body size 5~ 20mm 2. Radial lead resin coated 3. Broad operating voltage ... THINKING ELECTRONIC INDUSTRIAL Co., LTD. 3. TVR 05121 TVR 07121 TVR 10121 TVR 14121 TVR 20121 TVR 05151 TVR 07151
• Zinc Oxide Materials for Electronic and Optoelectronic Device ... — Zinc Oxide (ZnO) powder has been widely used as a white paint pigment and industrial processing chemical for nearly 150 years. However, following a rediscovery of ZnO and its potential applications in the 1950s, science and industry alike began to realize that ZnO had many interesting novel properties that were worthy of further investigation. ZnO is a leading candidate for the next generation ...
• Zinc Oxide Materials for Electronic and ... - Wiley Online Library — Cole W. Litton, the editor and compiler of Zinc Oxide Materials for Electronic and Optoelectronic Device Applications, died of a heart attack on Tuesday, January 26, 2010, while attending the SPIE Photonics West Conference in San Francisco.
• PDF Zinc oxide varistors - WEIDY — capability and non-linear electrical characteristics. The varistor is made of zinc oxide as a main body and a variety of metal oxides are added. After pressing and sintering, as shown in Fig. 2, a polycrystalline semiconductor ceramic module having grain boundary properties can be used to generate nonlinear current-voltage characteristics.
• PDF Zinc Oxide Varistor - Fenghua — ZINC OXIDE VARISTOR Are non-linear resistors utilize a semiconductor electronic ceramic element mainly composed of Zinc Oxide and its resistors change as a function of the applied voltage .It s called Varistor or Transient surge absorbers (18V~1.8KV) ( 25ns) (2000A/cm 2) Widely voltage range 18V~1.8KV Fast response to the rapidly increase ...
• PDF SIOV metal oxide varistors - TDK Electronics AG — possibility of using a single varistor with a higher load capacity should always be preferred, in this example it would be a type from the LS50, B60 or B80 series. Figure 5 Tolerance band of the SIOV-B40K275 1.5 Selection guide The choice of a varistor involves three main steps: Select varistors that are suitable for the operating voltage.
• PDF STABILITY OF ZINC OXIDE VARISTORS - Research Explorer The University of ... — STABILITY OF ZINC OXIDE VARISTORS A thesis submitted to the University of Manchester for the degree of Doctor of Philosophy in the Faculty of Engineering and Physical ...
• Zinc Oxide: Fundamentals, Materials and Device Technology — This first systematic, authoritative and thorough treatment in one comprehensive volume presents the fundamentals and technologies of the topic, elucidating all aspects of ZnO materials and devices. Following an introduction, the authors look at the general properties of ZnO, as well as its growth, optical processes, doping and ZnO-based dilute magnetic semiconductors. Concluding sections ...