What is a Schottky Diode?
A Schottky diode is a semiconductor device that utilizes a metal-semiconductor junction, known as the Schottky barrier, to achieve rectification. Unlike conventional p-n junction diodes, Schottky diodes are unipolar devices, relying solely on the majority carrier (electrons) for conduction.
Properties of Schottky Diode
- Barrier Height: The Schottky barrier height (SBH) is a critical parameter that determines the diode’s forward voltage drop and reverse leakage current. It depends on the metalwork function and semiconductor properties. Common SBH values range from 0.3-0.9 eV for Si and 0.6-1.6 eV for GaN. Metals with higher work functions, like Pt, yield higher SBHs for improved reverse blocking.
- Ideality Factor: The ideality factor (n) indicates how closely the diode follows the ideal thermionic emission theory. Values of n > 1 arise from effects like interface states, tunneling, and generation-recombination. Typical n values are 1.1-1.5 for high-quality Schottky diodes.
- Series Resistance: The parasitic series resistance (Rs) degrades performance, increasing the forward voltage drop. Rs depends on factors like the metal-semiconductor contact resistance and semiconductor doping. Low Rs (<10 Ω) is desired for efficient power devices.
- Reverse Leakage: Minimizing reverse leakage current reduces power dissipation, with SBH, tunneling, and high reverse bias edge effects impacting this parameter.
- Frequency Response: The capacitance decreases at higher frequencies due to minority carrier response time limitations, affecting the high-frequency and switching performance of Schottky diodes.
How Does Schottky Diode Work?
- Majority Carrier Transport: Unlike conventional p-n junction diodes, Schottky diodes are unipolar devices, relying solely on the transport of majority carriers (electrons in n-type semiconductors) across the metal-semiconductor interface. This eliminates the need for minority carrier injection and recombination, resulting in faster switching speeds and lower forward voltage drops.
- Schottky Barrier Formation: When a high-function metal contacts an n-type semiconductor with lower electron affinity, a potential barrier forms at the interface. This Schottky barrier enables electron flow from the semiconductor to the metal under forward bias but blocks it in reverse, enabling rectification.
- Thermionic Emission: Under forward bias, electrons in the semiconductor gain sufficient energy to overcome the Schottky barrier through thermionic emission, enabling current flow from the semiconductor to the metal. The barrier height, typically around 0.3-0.5 V for common metal-semiconductor combinations, determines the forward voltage drop and the turn-on voltage of the diode.
- Reverse Bias Characteristics: In reverse bias, the Schottky barrier increases, and the depletion region widens, inhibiting majority carrier flow. Schottky diodes, however, exhibit higher reverse leakage compared to p-n diodes due to the absence of minority carrier injection.
Pros and Cons of Schottky Diode
Pros of Schottky Diodes
- Low forward voltage drop: Schottky diodes have a lower barrier height at the metal-semiconductor junction, resulting in a smaller forward voltage required to turn on the device and allow current flow in the forward direction. This leads to lower power dissipation and higher efficiency compared to conventional p-n junction diodes.
- High switching speed: Schottky diodes are majority carrier devices and do not exhibit minority carrier behavior, which results in faster switching speeds and reduced switching losses. They have lower junction capacitance than p-n diodes, enabling high-frequency operation.
- Simple fabrication: Schottky diodes can be fabricated by forming a metal-semiconductor junction, which is a simpler process compared to the formation of p-n junctions. This can lead to lower manufacturing costs.
Cons of Schottky Diodes
- High reverse leakage current: Schottky diodes suffer from relatively high reverse leakage currents due to the lowering of the Schottky barrier under reverse bias conditions. This can degrade the rectification performance and increase power dissipation.
- Low reverse breakdown voltage: Conventional Schottky diodes have relatively low reverse-biased voltage ratings compared to p-n junction diodes, limiting their applications in high-voltage circuits.
- Temperature sensitivity: The reverse leakage current in Schottky diodes increases significantly at higher temperatures, negatively impacting their rectification properties and limiting their operation in high-temperature environments.
Applications of Schottky Diode
Power Electronics
Schottky diodes are extensively used in switched-mode power supplies, power converters, and rectifier circuits. Their low forward voltage drop results in reduced power dissipation and improved efficiency, making them suitable for power management applications.
Radio Frequency (RF) and Microwave Circuits
The high-speed switching capability and low junction capacitance of Schottky diodes make them ideal for RF and microwave applications, such as mixers, detectors, and frequency multipliers. They are widely employed in radar systems, satellite communications, and wireless communication devices.
Electrostatic Discharge (ESD) Protection
Schottky diodes offer superior ESD protection compared to conventional p-n junction diodes due to their lower capacitance and faster response time. They are commonly integrated into integrated circuits (ICs) to protect sensitive components from ESD events.
Voltage Clamping and Rectification
The low forward voltage drop and high reverse breakdown voltage of Schottky diodes make them suitable for voltage clamping and rectification applications. They are used in voltage clamping circuits to prevent overvoltage conditions and in rectifier circuits for AC-to-DC conversion.
Photodetection and Temperature Sensing
Schottky diodes exhibit photodetection and temperature sensing capabilities, enabling their use in optical communication systems and temperature monitoring applications. Their sensitivity to light and temperature variations allows for the development of integrated photodetectors and temperature sensors in CMOS technology.
Emerging Applications
With the advent of new technologies, Schottky diodes are finding applications in emerging fields such as millimeter-wave (mmWave) and terahertz (THz) circuits for 5G and beyond communication systems, as well as in power management for Internet of Things (IoT) devices and low-power system-on-chip (SoC) designs.
Application Cases
| Product/Project | Technical Outcomes | Application Scenarios |
|---|---|---|
| Monoclinic HfO2 Schottky Diode | Key components for improved electronic and optoelectronic functions | Electronic and optoelectronic applications requiring enhanced performance |
| CMOS Schottky Diode | Used for designing charge pump circuits and low-voltage reference circuits | Microwave power detection and low-voltage circuit applications |
| High-voltage Monolithic Schottky Device Power Integrations, Inc. | Supports high-voltage potential along the vertical thickness of the pillar | High-voltage applications in power electronics |
| Schottky Integrated High Voltage Terminations Infineon Technologies Americas Corp. | Provides high voltage isolation and protection | High voltage integrated circuits (HVIC) applications |
Latest Innovations of Schottky Diode
Novel Materials and Structures
- Silicon Schottky diodes with tungsten contacts instead of silicides, enabling 4x smaller junction area and potential to replace BJTs/p-n diodes in low-power SoCs and memory
- High-performance Ga2O3 Schottky diodes using SnOx Schottky contacts with Sn, SnO, and SnO2 components, achieving a barrier height of 1.19 eV and ideality factor of 1.02
- Single crystal diamond Schottky diodes with p+ doped thin δ-layers and p+ spots in the intrinsic layer, enhancing forward current density up to 40 A/cm2 for 2 kV devices
Fabrication Techniques
- Shallow trench contact process to reduce leakage current in silicon Schottky diodes
- Edge termination structures in SiC Schottky diodes to reduce perimeter leakage below the active area reverse current
- Novel LOCOS-based process for trench Schottky diodes with fewer mask layers
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