CN107819071B

CN107819071B - Planar Gunn millimeter wave and terahertz power amplifier and preparation method thereof

Info

Publication number: CN107819071B
Application number: CN201711046073.4A
Authority: CN
Inventors: 宋爱民; 王汉斌; 张翼飞; 王卿璞
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2017-10-31
Filing date: 2017-10-31
Publication date: 2020-05-05
Anticipated expiration: 2037-10-31
Also published as: CN107819071A

Abstract

The invention relates to a planar Gunn millimeter wave and terahertz power amplifier and a preparation method thereof, which sequentially comprises a substrate, a channel layer and a coplanar waveguide electrode from bottom to top, wherein the carrier concentration of the channel layer is 1 multiplied by 10¹⁴～1×10¹⁷cm^‑3The length of the channel layer is 1-10 mu m, and the value range of the product N of the carrier concentration of the channel layer and the length of the channel layer is 1 multiplied by 10¹¹cm^‑2＜N＜1×10¹⁴cm^‑2. The Gunn power amplifier with the planar structure has an obvious negative differential resistance effect, and can realize power amplification from microwave to terahertz frequency. The planar Gunn device is favorable for being used as a microwave or terahertz amplifier to be applied to the fields of microwave and terahertz communication, radar, imaging and the like.

Description

Planar Gunn millimeter wave and terahertz power amplifier and preparation method thereof

Technical Field

The invention relates to a planar gunn millimeter wave and terahertz power amplifier and a preparation method thereof, in particular to a high-frequency, high-gain and low-cost planar gunn diode amplifier, and belongs to the technical field of diodes in microwave devices.

Background

Solid-state millimeter wave and terahertz (30-3000GHz) power amplifiers have very important applications in many scientific and technological fields, such as high-speed broadband communication, medicine, radar, astronomy, security inspection and the like. However, power amplifiers capable of operating at such high frequencies are still mainly based on three-terminal devices such as high mobility field effect transistors (HEMTs) and bipolar heterojunction field effect transistors (HBTs). The operating frequency of a HEMT is inversely proportional to the channel length, and in order to realize that a HEMT can operate at a frequency of millimeter waves or even terahertz, the channel length has to be shortened to only tens of nanometers. Such a small channel size is a great challenge for device fabrication, with the consequence that high-frequency HEMT amplifiers are expensive and difficult to apply on a large scale, and it is therefore desirable to find a substitute for HEMTs. An HBT, although not requiring an extremely short channel, heats up significantly when operating, and is itself very temperature sensitive, so that its linearity and stability degrade dramatically when operating at higher power, resulting in its use only with small signals.

Two-terminal devices having differential negative resistance characteristics (NDR), such as an avalanche time-of-flight diode (IMPATT), a Resonant Tunneling Diode (RTD) and a Gunn diode (Gunn diode), were the earliest solid-state devices for microwave generation and power amplification. However, IMPATT and RTD are both very voltage sensitive and therefore non-linearity problems can also occur at high power.

Gunn, the Gunn diode, was originally discovered in 1963, and utilizes the differential negative resistance effect of electrons in certain semiconductor materials (such as GaAs, InP, GaN, etc.) when the electrons transit from low energy valley to high energy valley, because the effective mass of the electrons becomes larger and the saturation drift velocity decreases.

Gunn diodes are not sensitive to voltage, and therefore maintain good linearity at high power, as compared to other two terminal devices. And it also has the advantages of high working frequency, high gain, low noise, simple structure, long service life, low cost, etc., so it is widely regarded. Conventional gunns devices are also called vertical gunns devices because electrical contacts are made on the front and back sides of the semiconductor substrate and current flows perpendicular to the plane of the electrodes. The reported vertical Gunn diode amplifier has an operating frequency up to 94GHz and a power gain of 35 dB. But the improvement in performance of such vertical gunns diodes has encountered a bottleneck, the greatest difficulty of which is the joule heating effect. Since the operating frequency of a gunn device is inversely proportional to the channel length, the channel length of a high frequency gunn diode is generally required to be shortened to about 1 μm. Meanwhile, in order to ensure that the product of the channel length and the carrier concentration is more than 10¹²cm-²The carrier concentration in the channel is also increased. The result is a very high power density in the channel and significant heating during device operation. Excessive temperatures can cause breakdown of the channel leading to device failure. Although attempts have been made to lower the temperature of the device channel, including thinning the substrate to 2 μm and using a diamond heat sink, the fundamental frequency of gunn diodes can only reach 160GHz at the maximum at present. In addition to frequency limitations, vertical Gunn devicesThe device also has the defects of large packaging volume, incapability of integration and the like, and limits the application of the device in the fields of high frequency, integration and the like.

Planar gunns devices have in turn solved well the above-mentioned problems with vertical gunns devices. In planar gunns devices, the electrodes are on the same side of the semiconductor substrate and current flows in a direction parallel to the plane of the electrodes. Planar gunns devices do not have serious emission problems because the current density in their two-dimensional channels is much lower than that of the three-dimensional channels in vertical devices. This allows planar gunns devices to have shorter channels and thus operate at higher frequencies. The fundamental frequency of the present planar gunn devices with the highest frequency has reached 300GHz, which is nearly twice that of the vertical devices. Monte Carlo simulations confirmed that planar Gunn devices may operate even at frequencies of 1 THz. Besides higher frequency, the planar Gunn device also has the advantages of integration and adjustable frequency, and is very suitable for being applied to future monolithic microwave and terahertz integrated circuits (MMICs and MTICs). However, the planar gunn devices reported at present are limited to oscillators.

The applicant filed an invention named "a planar gunn diode with high power and low noise and a method for manufacturing the same" on 2017, 3, 17, and the planar gunn diode comprises an insulating substrate, a channel layer and a coplanar waveguide arranged on the channel layer, wherein the length of a resonant cavity of the coplanar waveguide is an integral multiple of one-half of a resonant wavelength, and the characteristic impedance of the coplanar waveguide at a resonant frequency is equal to the impedance of a load (generally 50 ohms). The planar Gunn diode of the present invention is placed in the coplanar waveguide resonant cavity, so that the planar Gunn device can work in a resonant mode, the transmitting power, the conversion efficiency and the frequency stability of the planar Gunn device are greatly improved, and the phase noise is reduced. However, this patent relates to an oscillator that generates an electromagnetic wave signal of a specific frequency during operation, and cannot amplify the signal.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a planar Gunn millimeter wave and terahertz power amplifier;

the invention also provides a preparation method of the power amplifier;

the power amplifier has the characteristics of high frequency, high gain and simple structure.

The technical scheme of the invention is as follows:

a planar Gunn millimeter wave and terahertz power amplifier sequentially comprises a substrate, a channel layer and a coplanar waveguide electrode from bottom to top, wherein the carrier concentration of the channel layer is 1 multiplied by 10¹⁴～1×10¹⁷cm^-3The length of the channel layer is 1-10 mu m, and the value range of the product N of the carrier concentration of the channel layer and the length of the channel layer is 1 multiplied by 10¹¹cm^-2＜N＜1×10¹⁴cm^-2。

The principle of operation of planar gunn power amplifiers is the amplification of ac signals by the differential negative resistance in the gunn effect. The carrier concentration of the channel layer of the device, the length of the channel layer and the product N of the carrier concentration and the length of the channel layer all have the influence on the power amplification performance of the device. Too low a carrier concentration in the channel layer may result in increased internal resistance and reduced negative resistance characteristics of the device, and reduced output power and conversion efficiency. And too high concentration can result in too high current density, severe heating and reduced device life. Meanwhile, too high carrier concentration often means higher doping concentration, and too much impurities affect the appearance of gunn effect, so that negative resistance characteristics disappear, and the device fails. The product N of the carrier concentration of the channel layer and the length of the channel layer affects the operating mode of the gunn amplifier, and exceeding the product by a limited range may result in the reduction or even disappearance of the power amplification capability.

Compared with the existing power amplifier, the planar Gunn device has the advantages of high working frequency, large output power, simple preparation process, low cost and integration.

Preferably, according to the invention, the characteristic impedance of the coplanar waveguide electrode is 50 Ω.

50 ohms is the most widely used impedance value in microwave circuits. The characteristic impedance of the coplanar waveguide electrode is 50 omega, so that impedance matching with the front-end and rear-end devices is realized, and microwave power transmission efficiency is improved.

According to the invention, a buffer layer with the thickness of 50 nm-5 μm is preferably epitaxially grown on the substrate, and the buffer layer is made of undoped InP, GaAs, AlAs, GaN, AlN, InAlN, AlGaN, InAlAs or AlGaAs.

The design has the advantages that the influence of lattice defects in the substrate and impurities from the substrate on the channel layer is reduced, and the quality of the channel layer is improved. The buffer layer is selected to have a good lattice match with the underlying substrate and the epitaxial material thereon, and is inherently highly resistive.

According to the invention, a cap layer with the thickness of 5-300 nm is epitaxially grown on the channel layer, an ohmic contact electrode is arranged on the cap layer, the cap layer is made of heavily doped semiconductor materials, the heavily doped semiconductor materials comprise InP, GaAs, InGaAs, InAs, InGaAsP, GaN, InGaN and InAlN, and the concentration of carriers of the cap layer at room temperature (25 ℃) is more than 1 multiplied by 10¹⁸cm^-3。

The design has the advantages of reducing the contact resistance of the electrode and protecting the channel layer. The carrier concentration of the cap layer is more than 1 multiplied by 10¹⁸cm^-3In the process, the electrode metal and the carriers in the cap layer can easily cross the surface potential barrier in a tunneling mode, so that the contact resistance is far smaller than the case that the carrier concentration of the cap layer is lower.

According to the invention, the substrate is made of semi-insulating InP, semi-insulating GaAs, SiC, sapphire or high-resistance silicon;

the channel layer is a layer of uniform semiconductor material or a plurality of layers of semiconductor materials; the semiconductor material is one or more of III-V group binary compounds and multi-element compounds, and the III-V group binary compounds comprise InP, GaAs, InAs, GaN and InN; the multi-component compound comprises InGaAs, InAlAs, AlGaAs, InGaN, InAlN, AlGaN and InGaAsP; the thickness of the channel layer is 10 nm-1 um.

Too thin channel thickness can cause too large internal resistance, and carrier migration in the channel can be influenced by the channel layer interface, thus causing mobility reduction, high-frequency performance reduction and the like. Too thick channel layer can lead to too little internal resistance, and the device generates heat seriously, and the life-span reduces.

The coplanar waveguide electrode or the ohmic contact electrode is made of one or more of Au, Ge, Ni, Ti, Al, Pd, Pt, Mo, In, Ga and Ag, and the thickness of the coplanar waveguide electrode is more than three times of the skin depth. The thickness of the coplanar waveguide electrode is greater than 0.2 μm.

When the thickness of the electrode is equal to three times of the skin depth, the effect of continuously increasing the thickness of the electrode on reducing the internal resistance of the electrode is not great, but the reduction of the thickness of the electrode can obviously increase the resistance of the electrode, so that the transmission loss of the alternating current signal is increased. The skin depths of alternating current signals with different frequencies are different, and the skin depth is smaller when the frequency is higher. Therefore, for planar gunn power amplifiers, the thickness of the coplanar waveguide electrode should be more than three times of the lower limit of the operating frequency.

The working process of the planar Gunn millimeter wave and terahertz power amplifier comprises the following steps:

A. applying a direct current bias voltage to the planar Gunn amplifier through a direct current bias network to enable the working point of the planar Gunn amplifier to be positioned in a differential negative resistance region;

B. inputting a microwave signal with a certain frequency through the input end of the planar gunn amplifier;

C. and outputting the microwave signal with unchanged frequency and increased power at the output end of the planar Gunn amplifier.

The preparation method of the planar Gunn power amplifier comprises the following specific steps:

(1) epitaxially growing a buffer layer, a channel layer and a cap layer on a substrate in sequence;

(2) forming a table top on the sample generated in the step (1) by using a micro-nano processing method; realizing electrical isolation among devices;

(3) removing the cap layer on the sample generated in the step (2) by using a micro-nano processing method to expose the channel;

(4) and (4) sequentially preparing an ohmic contact electrode and a coplanar waveguide electrode on the sample generated in the step (3) by using a micro-nano processing method.

According to the present invention, preferably, the step (3) specifically refers to: and removing the cap layer of the channel part by using a micro-nano processing method, and taking the rest of the cap layer or the rest of the cap layer as a channel layer.

According to the present invention, preferably, the step (4) specifically refers to:

a. preparing an ohmic contact electrode with a pattern by using a micro-nano processing method;

b. and preparing the coplanar waveguide electrode with the graph by using a micro-nano processing method.

The invention has the beneficial effects that:

the Gunn power amplifier with the planar structure has an obvious negative differential resistance effect, and can realize power amplification from microwave to terahertz frequency. The planar Gunn device is favorable for being used as a microwave or terahertz amplifier to be applied to the fields of microwave and terahertz communication, radar, imaging and the like.

Drawings

Fig. 1 is a schematic structural diagram of a power amplifier according to the present invention;

FIG. 2 is a graph illustrating a power gain test result curve of a power amplifier with channel layer lengths of 2, 4 and 6 μm at a frequency of 6-67 GHz;

FIG. 3 is a graph illustrating the power gain test result curves of power amplifiers with channel layer lengths of 2, 4 and 6 μm at frequencies of 75-110 GHz;

FIG. 4 is a diagram showing a test result curve of a power amplifier with a channel layer length of 4 μm under DC bias voltages of 2.9V and 4.0V respectively for power gain variation with input signal power;

1. the semiconductor device comprises a substrate, a buffer layer, a channel layer, a cap layer, a buffer layer, a channel layer, a cap layer, a channel layer.

Detailed Description

The invention is further defined in the following, but not limited to, the figures and examples in the description.

Example 1

A planar Gunn millimeter wave and terahertz power amplifier comprises a substrate 1, a buffer layer 2, a channel layer 3, a cap layer 4 and an ohmic contact electrode from bottom to top in sequence as shown in figure 1Electrode 5, coplanar waveguide electrode 6, and channel layer 3 having a carrier concentration of 8 × 10¹⁶cm^-3The length of the channel layer 3 is 4 μm, and the value of the product N of the carrier concentration of the channel layer 3 and the length of the channel layer 3 is 3.2 × 10¹³cm^-2。

The principle of operation of planar gunn power amplifiers is the amplification of ac signals by the differential negative resistance in the gunn effect. The carrier concentration of the device channel layer 3, the length of the channel layer 3, and the product N of the carrier concentration and the length of the channel layer 3 all have an effect on the device power amplification performance. Too low carrier concentration in the channel layer 3 results in increased internal resistance of the device, reduced negative resistance characteristics, and reduced output power and conversion efficiency. And too high concentration can result in too high current density, severe heating and reduced device life. Meanwhile, too high carrier concentration often means higher doping concentration, and too much impurities affect the appearance of gunn effect, so that negative resistance characteristics disappear, and the device fails. The product N of the carrier concentration of the channel layer 3 and the length of the channel layer 3 affects the operation mode of the gunn amplifier, and exceeding the product by a limited range may result in a decrease or even a disappearance of the power amplification capability.

The characteristic impedance of the coplanar waveguide electrode 6 is 50 Ω.

50 ohms is the most widely used impedance value in microwave circuits. The characteristic impedance of the coplanar waveguide electrode 6 is 50 Ω, which is to realize impedance matching with the front and rear devices and to provide microwave power transmission efficiency.

The thickness of the buffer layer 2 is 50 nm-5 μm, and the buffer layer 2 is made of undoped InP, GaAs, AlAs, GaN, AlN, InAlN, AlGaN, InAlAs or AlGaAs.

The thickness of the cap layer 4 is 5-300 nm, the cap layer 4 is made of heavily doped semiconductor materials, the heavily doped semiconductor materials comprise InP, GaAs, InGaAs, InAs, InGaAsP, GaN, InGaN and InAlN, and the concentration of the current in the cap layer at 425 ℃ is more than 1 multiplied by 10¹⁸cm^-3. The electrode contact resistance is reduced, and the channel layer 3 is protected.

The advantage of this design is that the electrode contact resistance is reduced, protecting the channel layer 3. The carrier concentration of the cap layer 4 is more than 1 multiplied by 10¹⁸cm^-3In the process, the electrode metal and the carriers in the cap layer 4 can easily cross the surface potential barrier in a tunneling mode, so that the contact resistance is far smaller than the case that the carrier concentration of the cap layer 4 is lower.

The substrate 1 is made of semi-insulating InP, semi-insulating GaAs, SiC, sapphire or high-resistance silicon;

the channel layer 3 is a layer of uniform semiconductor material or a plurality of layers of semiconductor materials; the semiconductor material is one or more of III-V group binary compounds and multi-element compounds, and the III-V group binary compounds comprise InP, GaAs, InAs, GaN and InN; the multicomponent compound comprises InGaAs, InAlAs, AlGaAs, InGaN, InAlN, AlGaN and InGaAsP; the thickness of the channel layer 3 is 300 nm. Too thin thickness of the channel layer 3 may result in too large internal resistance, and carrier migration in the channel may be affected by the interface of the channel layer 3, resulting in reduced mobility, reduced high frequency performance, and the like. Too thick channel layer 3 may result in too little internal resistance, severe device heating, and reduced lifetime.

The coplanar waveguide electrode 6 or the ohmic contact electrode 5 is made of one or more of Au, Ge, Ni, Ti, Al, Pd, Pt, Mo, In, Ga, and Ag, and the thickness of the coplanar waveguide electrode 6 is 2 μm.

Fig. 4 is a graph illustrating a test result curve of the power gain of the power amplifier according to embodiment 1 varying with the power of the input signal under dc bias voltages of 2.9V and 4.0V, respectively; the 1dB compression points of the device are 0dBm and-4 dBm, respectively. This reflects the feature that the planar gunn power amplifier still maintains good linearity under large signal conditions.

Example 2

The difference between the planar gunn millimeter wave and terahertz power amplifier according to embodiment 1 is that the length of the channel layer 3 is 2 μm, and the value of the product N of the carrier concentration of the channel layer 3 and the length of the channel layer 3 is 1.6 × 10¹³cm^-2。

Example 3

A flat surface according to embodiment 1The gunn millimeter wave and terahertz power amplifier is characterized in that the length of the channel layer 3 is 6 microns, and the value of the product N of the carrier concentration of the channel layer 3 and the length of the channel layer 3 is 4.8 multiplied by 10¹³cm^-2。

FIG. 2 is a graph illustrating a power gain test result curve of a power amplifier with channel layer lengths of 2, 4 and 6 μm at a frequency of 6-67 GHz; FIG. 3 is a graph illustrating the power gain test result curves of power amplifiers with channel layer lengths of 2, 4 and 6 μm at frequencies of 75-110 GHz; the peak gain reaches 17dB, and the highest working frequency exceeds 110 GHz. Reflecting the characteristics of high frequency and high gain of the power amplifier.

Example 4

The method for fabricating a planar gunn power amplifier according to any one of embodiments 1 to 3, comprising the steps of:

(1) sequentially epitaxially growing a buffer layer 2, a channel layer 3 and a cap layer 4 on a substrate 1;

(3) removing the cap layer 4 on the sample generated in the step (2) by using a micro-nano processing method to expose a channel; the method specifically comprises the following steps: and removing the cap layer 4 of the channel part by using a micro-nano processing method, and taking the rest of the cap layer as the channel layer 3.

(4) And (4) sequentially preparing an ohmic contact electrode 5 and a coplanar waveguide electrode 6 on the sample generated in the step (3) by using a micro-nano processing method. The method specifically comprises the following steps:

a. preparing an ohmic contact electrode 5 with a graph by using a micro-nano processing method;

b. the coplanar waveguide electrode 6 with the graph is prepared by a micro-nano processing method.

Claims

1. A planar Gunn millimeter wave and terahertz power amplifier is characterized by sequentially comprising a substrate, a channel layer and a coplanar waveguide electrode from bottom to top, wherein the carrier concentration of the channel layer is 8 multiplied by 10¹⁶～1×10¹⁷cm^-3The length of the channel layer is 4-10 mu m, and the current carrying of the channel layerThe product N of the sub-concentration and the length of the channel layer has a value range of 3.2 × 10¹³cm^-2＜N＜1×10¹⁴cm^-2(ii) a The characteristic impedance of the coplanar waveguide electrode is 50 Ω.

2. The planar gunn millimeter wave and terahertz power amplifier according to claim 1, wherein the substrate is epitaxially grown with a buffer layer with a thickness of 50nm to 5 μm, and the buffer layer is made of undoped InP, GaAs, AlAs, GaN, AlN, InAlN, AlGaN, InAlAs or AlGaAs.

3. The planar Gunn millimeter wave and terahertz power amplifier according to claim 2, wherein the channel layer is epitaxially grown with a cap layer with a thickness of 5-300 nm, the cap layer is provided with an ohmic contact electrode, the cap layer is made of a heavily doped semiconductor material, the heavily doped semiconductor material comprises InP, GaAs, InGaAs, InAs, InGaAsP, GaN, InGaN and InAlN, and the cap layer has a carrier concentration of more than 1 x 10 at room temperature¹⁸cm^-3。

4. The planar Gunn millimeter wave and terahertz power amplifier according to any one of claims 1 to 3, wherein the material of the substrate is semi-insulating InP, semi-insulating GaAs, SiC, sapphire or high-resistance silicon;

the channel layer is a layer of uniform semiconductor material or a plurality of layers of semiconductor materials; the semiconductor material is one or more of III-V group binary compounds and multi-element compounds, and the III-V group binary compounds comprise InP, GaAs, InAs, GaN and InN; the multi-component compound comprises InGaAs, InAlAs, AlGaAs, InGaN, InAlN, AlGaN and InGaAsP; the thickness of the channel layer is 10 nm-1 um;

the coplanar waveguide electrode or the ohmic contact electrode is made of one or more of Au, Ge, Ni, Ti, Al, Pd, Pt, Mo, In, Ga and Ag, and the thickness of the coplanar waveguide electrode is more than three times of the skin depth; the thickness of the coplanar waveguide electrode is greater than 0.2 μm.

5. The method for fabricating a planar gunn power amplifier as claimed in claim 4, wherein the concrete steps comprise:

(2) forming a table top on the sample generated in the step (1) by using a micro-nano processing method;

6. The fabrication method of a planar gunn power amplifier according to claim 5, wherein said step (3) comprises: and removing the cap layer of the channel part by using a micro-nano processing method, and taking the rest of the cap layer or the rest of the cap layer as a channel layer.

7. The fabrication method of the planar gunn power amplifier according to claim 5 or 6, wherein said step (4) comprises: