Microwave Diode: Introduction and Types

Catalog

I. Introduction

Diodes are used in electronic circuits, integrated circuits, and electronic devices in computers. For example, diodes and transistors are a combination of P-type and N-type semiconductor materials. Diodes are an example of the P-N type and are widely used in electronics.

Figure 1 shows the changes that occur when the P-type and N-type semiconductor materials are combined. A large number of electrons in the N-type material pass through the conduction band and enter the electron holes in the valence band of the P-type material.

Each electron eliminates an electron-hole, the N-type loses energy to the P-type and reaches a balance. The electrons must pass through the junction when flowing through the system, and the energy of a lower voltage can be applied to control the current.

Various diodes in the microwave field, including varactor diodes, step diodes, PIN diodes, limiting diodes, electrically modulated varactor diodes, solid noise diodes, and avalanche diodes. Various microwave diodes play the roles of low-noise amplification, power generation, frequency conversion, modulation, demodulation, and signal control in microwave circuits.

Microwave diodes are diodes that mainly work in the microwave frequency band. Such as barrier injection transit time diode (BARITT), impact avalanche transit time diode (IMPATT), limited space-charge accumulation diode (LSA), Gunn diode (Gunn), trapped plasma avalanche diode (TRAPATT), and varactor diode Wait. All of these diodes use the negative resistance effect to directly convert DC electrical energy into radiant microwave energy.

Microwave diodes are various diodes in the microwave field. Among them, the working frequency range of the microwave detector diode is 0-40GHz, and the detection tangent sensitivity is 45-55dB·μW. The step diode combined with the quartz crystal oscillator can stabilize the frequency of the microwave source to the order of 10-6 to 10-9.

After the discovery of the point-contact diode effect at the end of the 19th century, microwave diodes such as PIN diodes, varactor diodes, Schottky diodes, tunnel diodes, Gunn diodes, etc. appeared one after another. The substrate materials of microwave diodes have developed from germanium and silicon to gallium arsenide, which has continuously improved the working frequency of microwave diodes, and the current maximum frequency has reached 300 GHz. Microwave diodes have the advantages of small size and high reliability, and are used in microwave oscillation, amplification, frequency conversion, switching, phase shifting, and modulation.

Microwave diode is the general term for various diodes working in the microwave field. According to its function at work, it can be divided into low noise receiving device, control device, and microwave power source device. Commonly used low-noise receiving devices are point contact diodes, Schottky barrier diodes, tunnel diodes, and parametric varactor diodes, etc.; for control devices, there are electrically tuned varactor diodes, high-frequency switching diodes, and pin diodes; and power Varactor diodes, body effect diodes, step recovery diodes, and avalanche diodes can be used as microwave power source devices.

II. Types

1. IMPact Ionization Avalanche Transit-Time Diode (IMPATT Diode)

IMPATT Diode is a diode made based on the principle of PN junction reverse avalanche multiplication and radiofrequency negative resistance generated by the transition. It was proposed by W.T. Reid in 1958, so it is also called Reid diode. This type of diode has various structures: Reed structure (ie P+NIN+), Schottky structure (M-N-N+) high-low-high structure (H-L-H), double drift structure (DDR or P+PNN+), etc. The materials used are mainly silicon and gallium arsenide. In addition to the PN junction avalanche transit diode, due to the difference in its working mechanism, there are also trapped plasma avalanche trigger transit time diodes, metal-semiconductor-metal barrier transit diodes, and tunnel avalanche transit diodes. The avalanche crossing diode and its power source can reach extremely high operating frequencies, from several hundred MHz to 300 GHz, a certain microwave power can be obtained. Especially in the millimeter-wave band, it is the most powerful solid-state device in modern times, which can work in continuous waves or pulse. The disadvantage is that the noise is slightly higher than that of electron transfer devices. Avalanche oscillators and lock-in amplifiers made of avalanche transit diodes are used in microwave communications, radar, and tactical missiles.

This type of diode uses the combination of avalanche phenomenon and transit time effect in the semiconductor to obtain dynamic negative resistance, thereby generating microwave oscillation. Avalanche diodes are used as oscillator tubes, parametric amplifier pump sources, etc.

The materials currently used in avalanche diodes are mainly Si and GaAs, and they can also be made of InP or other materials. Among them, Si material has better device characteristics. In order to dissipate heat, most of these devices use flip-chip structures and diamond heat sinks. Avalanche diodes are currently the most powerful and efficient solid-state power devices in millimeter-wave or even sub-millimeter wave frequency bands, and their highest oscillation frequency can reach 400 GHz. The current millimeter-wave power IMPATT, the output pulse power at 92G~96GHz is ≥20W; the pulse power at 118GHz is 22W, and the DC-RF efficiency is 15%.

2. Schottky Barrier Diode

Schottky barrier diodes usually use N-semiconductor materials. This kind of device frequency bandwidth is an important microwave and millimeter-wave receiving device, including mixers, detectors, etc. The beam-leaded Schottky barrier diode is a planar structure device, and the contact inductance is controlled in a low range, thereby minimizing the parasitic parameters caused by the device package. Its operating frequency ranges from several hundred MHz to 300 GHz, with features such as low noise, wide frequency bandwidth, and good anti-burnout performance. The noise figure of a microwave receiver that is directly mixed with diodes in the entire microwave frequency band is 4.0 to 70 decibels.

3. Gunn Diode

Gunn Diode, also known as body effect diode. The working mechanism of this type of device is based on an electron transfer effect. It uses the carriers in the semiconductor (electrons in N-type GaAs) to obtain energy in an external electric field, and transfers from the main energy band with high mobility to the sub-band with low mobility and high energy state, forming a differential resistance, thus producing Microwave oscillation. Gunn diodes have lower operating voltage and lower FM noise and are suitable for making local oscillator sources, signal sources, and low-power emission sources.

The materials used in Gunn diodes are III-V group compound semiconductors. At present, it is mainly GaAs and InP, but the GaAs Gunn diode operating frequency is below 100GHz millimeter-wave band, above which the output power will drop sharply. Because the speed-electric field characteristic of InP material has a higher peak-to-valley ratio and threshold electric field than GaAs, InP Gunn diodes have better frequency, power, efficiency, and noise performance.

4. Varactor Diode

Varactor diodes are made based on PN junction capacitance changing with reverse bias voltage. It can be roughly divided into two categories: varactors for low-noise parametric amplifiers and varactors for electrical tuning. The former is used for microwave parametric amplifiers, with a noise temperature as low as 30K, and has been widely used in satellite earth stations. The latter is mainly used for frequency tuning, voltage-controlled oscillators, electronic countermeasures, and rapid frequency agile radar frequency modulation. In addition, the varactor can also be used for phase shifting and amplitude limiting. In terms of production, there are certain differences between the two types of devices. The parametric varactor must have good capacitance nonlinearity and a high figure of merit; while the electrically tuned varactor must strictly control the doping concentration distribution of the semiconductor epitaxial layer in order to obtain a Large capacitance change area, and should have a higher figure of merit.

The characteristic of the varactor diode is that the junction capacitance that changes with the applied voltage provides variable reactance characteristics, and can be used as a lossless nonlinear element in the circuit. It is suitable for application in microwave signal modulation, harmonic generation (up-conversion), pulse generation and formation, etc., to make solid-state parametric amplifiers, harmonic generators, mixers, or frequency converters.

5. PIN Diode

A PIN diode is a variable resistance device, also known as a plasma diode. It is generally composed of P+P-I-NN+ multilayer semiconductors. The physical quantities and geometric parameters of the I layer can be controlled according to different uses. When the PIN diode is in the forward direction since the P and N layers respectively inject holes and electrons into the I layer, the electrons and holes form a plasma in the I layer and are in a low microwave impedance state. The equivalent small capacitance is a high microwave impedance state. PIN diodes can be used for microwave switching, ESC attenuation, phase shifting, microwave modulation, and other special purposes.