Diamond amplifier and electromechanical instrument

Abstract

The present invention contributes to improving performance while reducing the number of processes and having reduced size. This diamond amplifier comprises: an amplification circuit including at least one diamond transistor in which a source electrode, a drain electrode, and a gate electrode are arranged on a diamond semiconductor layer; and one or both of an input matching circuit connected to the input side of the amplification circuit and an output matching circuit connected to the output side of the amplification circuit.

Description

Diamond amplifiers and electrical machinery and equipment

[0001] The present invention relates to diamond amplifiers and electromechanical devices.

[0002] In recent years, with the increasing capacity and sophistication of communications, high reliability and low latency are required for amplifiers (e.g., monolithic microwave integrated circuits (MMICs) for high-frequency amplification) used in mobile base stations. With existing silicon amplifiers using silicon transistors, it has become difficult to demonstrate performance due to the temperature rise that accompanies the increasing capacity and sophistication of communications.

[0003] Against this background, wide bandgap semiconductor transistors using wide bandgap semiconductors such as GaN and SiC, which have wider bandgaps than silicon, have come into use, and wide bandgap semiconductor amplifiers using wide bandgap semiconductor transistors have been put to use. However, even with wide bandgap semiconductor amplifiers, as the power density increases, heat cannot be dissipated during high-load operation, and performance degradation due to temperature rise has become a major problem.

[0004] Therefore, Patent Document 1 proposes to overcome the performance degradation by stacking a first heat dissipation layer (diamond, aluminum nitride, etc.), an adhesive layer (gold-tin, gold-germanium, etc.), a second heat dissipation layer (diamond, aluminum nitride, etc.), and a metal medium (copper, aluminum, etc.) on the GaN die to improve heat dissipation.

[0005] Japanese Patent No. 6527666, Japanese Patent Application Laid-Open No. 2007-234911

[0006] The following analysis is provided by the present inventors.

[0007] However, if the structure of improving heat dissipation is newly added as in Patent Document 1, the process is increased, the size is increased, and it is not preferable from the viewpoint of operation efficiency.Therefore, Patent Document 2 proposes the diamond amplifier that uses diamond, which has higher thermal conductivity than wide band gap semiconductors such as GaN and SiC.However, in Patent Document 2, a highly boron-doped diamond layer is formed on a diamond substrate as source and drain, and an undoped diamond layer is provided between the highly boron-doped diamond layers as channel region, and the undoped diamond layer is covered with gate insulating film.Therefore, the undoped diamond layer only has the channel length or gate length on the diamond substrate between the highly boron-doped diamond layers, so heat dissipation does not progress, and the highly boron-doped diamond layer has lower thermal conductivity than the undoped diamond layer, which may reduce heat dissipation, and performance (high temperature performance, high pressure resistance performance, high frequency performance, high output performance, etc.) may be reduced. Furthermore, the system is complicated because it is equipped with a temperature control unit that maintains the temperature of the device at a constant temperature, and because it does not include matching circuits for input and output, it is difficult to perform amplification in the high frequency range, and there is a possibility that performance (high temperature performance, high voltage resistance performance, high frequency performance, high output performance, etc.) will be reduced.

[0008] The main object of the present invention is to provide a diamond amplifier and electromechanical device that can contribute to improving performance while reducing processes and miniaturizing.

[0009] The diamond amplifier according to the first aspect comprises an amplifier circuit including at least one diamond transistor having a source electrode, a drain electrode, and a gate electrode arranged on a diamond semiconductor layer, and one or both of an input matching circuit connected to the input side of the amplifier circuit and an output matching circuit connected to the output side of the amplifier circuit.

[0010] An electrical device according to a second aspect includes the diamond amplifier according to the first aspect.

[0011] The first and second aspects can contribute to improving performance while reducing the number of processes and miniaturizing the device.

[0012] 1 is a block diagram schematically showing an example of the configuration of a diamond amplifier according to embodiment 1. FIG. 2 is a block diagram schematically showing an example of the configuration of a millimeter-wave band communication device to which the diamond amplifier according to embodiment 1 is applied. FIG. 3 is a cross-sectional view schematically showing a first example of the configuration of a diamond transistor in the diamond amplifier according to embodiment 1. FIG. 4 is a cross-sectional view schematically showing a second example of the configuration of a diamond transistor in the diamond amplifier according to embodiment 1. FIG. 5 is a cross-sectional view schematically showing a third example of the configuration of a diamond transistor in the diamond amplifier according to embodiment 1. FIG. 6 is a cross-sectional view schematically showing a fourth example of the configuration of a diamond transistor in the diamond amplifier according to embodiment 1. FIG. 7 is a cross-sectional view schematically showing a fifth example of the configuration of a diamond transistor in the diamond amplifier according to embodiment 1. FIG. 8 is a cross-sectional view schematically showing a sixth example of the configuration of a diamond transistor in the diamond amplifier according to embodiment 1. FIG. 9 is a cross-sectional view schematically showing the configuration of a diamond transistor according to a comparative example. FIG. 10 is a table comparing the electrical conductivities of a boron-doped diamond layer and a hydrogen-terminated diamond semiconductor layer. FIG. 11 is a graph showing the relationship between the gate length and cutoff frequency of the diamond transistor in the diamond amplifier according to embodiment 1. FIG. 12 is a graph showing the relationship between the diamond substrate thickness of an MMIC and the temperature of the amplifier section. Graph showing the relationship between the thermal conductivity of the MMIC substrate and the temperature of the amplifier section. (A) A block diagram showing a schematic example of the configuration of a diamond amplifier according to embodiment 2, and (B) a cross-sectional view showing a schematic example of the configuration of a diamond transistor in the diamond amplifier. Graph showing an example of a Jds-Vds characteristic curve after heating to 300°C in an air atmosphere. Jds represents the drain current density, and Vds represents the drain bias voltage. Source: Appl. Phys. Lett. 118, 162105 (2021); doi: 10.1063 / 5.0040645 Submitted: 15 December 2020. Accepted: 31 March 2021. Published Online: 20 April 2021. Graph showing an example of a Jds-Vds characteristic curve after irradiation with 1 MGy in an air atmosphere.

[0013] The following description of the embodiments will be made with reference to the drawings. Note that, when drawing reference symbols are used in this application, they are intended solely to aid understanding and are not intended to limit the present invention to the illustrated embodiments. Furthermore, the following embodiments are merely examples and do not limit the present invention. Furthermore, connecting lines between blocks in the drawings and the like referred to in the following description include both bidirectional and unidirectional lines. Unidirectional arrows are used to schematically indicate the flow of the main signal (data) and do not exclude bidirectionality.

[0014] [Form 1] A diamond amplifier according to Form 1 will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic example of the configuration of a diamond amplifier according to Form 1. FIG. 2 is a block diagram showing a schematic example of the configuration of a millimeter-wave band communication device to which the diamond amplifier according to Form 1 is applied. FIGS. 3 to 8 are cross-sectional views showing first to sixth examples of the configuration of a diamond transistor in the diamond amplifier according to Form 1. FIG. 9 is a cross-sectional view showing a schematic example of the configuration of a diamond transistor according to a comparative example. FIG. 10 is a table comparing the electrical conductivities of a boron-doped diamond layer and a hydrogen-terminated diamond semiconductor layer. FIG. 11 is a graph showing the relationship between the gate length and cutoff frequency of the diamond transistor in the diamond amplifier according to Form 1. FIG. 12 is a graph showing the relationship between the thickness of the diamond substrate of an MMIC and the temperature of the amplifier section. FIG. 13 is a graph showing the relationship between the thermal conductivity of the MMIC substrate and the temperature of the amplifier section.

[0015] The diamond amplifier 20 is an amplifier that uses a diamond transistor 30 (see Figure 1). When used as an RF (Radio Frequency) amplifier, the diamond amplifier 20 can be configured to include an input matching circuit 21, an amplifier circuit 22 including a diamond transistor 30, and an output matching circuit 23, as shown in Figure 1, taking into account the effects of radio wave reflection in the high frequency range. The input matching circuit 21, the amplifier circuit 22, and the output matching circuit 23 may be configured on a single diamond substrate, forming an MMIC (Monolithic Microwave Integrated Circuit).

[0016] The input matching circuit 21 is a matching circuit connected to the input side of the amplifier circuit 22 (see FIG. 1). The input matching circuit 21 may be unnecessary depending on the application of the diamond amplifier 20. The input matching circuit 21 is preferably provided to properly receive the input signal. The input matching circuit 21 matches the impedance of the receiving side (input side) with the impedance of the sending side (amplifier circuit 22 side) to maximize (maximize) the input power (signal) and output it. The input matching circuit 21 can be configured, for example, using a resistive element in which a meander-shaped resistive layer made of a resistive material (e.g., nichrome, manganin, geranin, etc.) is formed on a diamond substrate. The resistive element of the input matching circuit 21 can be formed using the same process as the resistive element of the output matching circuit 23. The input matching circuit 21 can be configured to have an impedance of 1 Ω to 100 Ω, with an impedance of 50 Ω as a guideline, and preferably has an impedance of 45 to 55 Ω. Fabricating MMICs with matching circuit impedances that are within a certain degree of variation, typically around 50 Ω, enables the fabrication of more practical MMICs. Furthermore, aligning the matching circuit impedance to 50 Ω ensures standardization, compatibility, minimal loss, and signal integrity. 50 Ω is a widely adopted standard characteristic impedance for matching circuits, allowing for easy integration into existing systems, minimizing signal transmission loss, and maintaining signal integrity. By aligning the impedance of an MMIC's matching circuit between 1 and 100 Ω, a wide range of applicability is achieved. This range covers the characteristic impedance of transmission lines used in many common communications and electronic devices, allowing for flexible application to different systems and applications. By aligning the impedance of an MMIC's matching circuit between 45 and 55 Ω, practical matching can be achieved while allowing for some product variation and improving productivity.

[0017] The amplifier circuit 22 is an electronic circuit that amplifies and outputs input power (signal) (see FIG. 1). The amplifier circuit 22 is connected between the input matching circuit 21 and the output matching circuit 23. The amplifier circuit 22 can be configured to include at least one diamond transistor 30. The amplifier circuit 22 amplifies the input power (signal) using the diamond transistor 30 and outputs it. The configuration of the diamond transistor 30 will be described later.

[0018] The output matching circuit 23 is a matching circuit connected to the output side of the amplifier circuit 22 (see FIG. 1). The output matching circuit 23 may not be necessary depending on the application of the diamond amplifier 20. The output matching circuit 23 can be provided depending on the space and design concept. The output matching circuit 23 matches the impedance of the receiving side (amplifier circuit 22 side) and the impedance of the sending side (output side), maximizing the input power (signal) and outputting it with maximum efficiency. The output matching circuit 23 can be configured similarly to the input matching circuit 21.

[0019] Diamond amplifier 20 can be used in electrical machinery and equipment such as terminals, devices, equipment, and facilities in the communications field, where the amount of data in the communications trunk networks connecting mobile base stations is rapidly increasing with the rapid expansion of high-speed data communications services such as smartphones. Diamond amplifier 20 can also be used in electrical machinery and equipment such as on-board devices and satellite communications systems in the automotive and satellite fields, which efficiently transmit large amounts of data and utilize broadband. Diamond amplifier 20 can also be used in electrical machinery and equipment such as military radar and communications systems in the defense field, where long-distance communications and highly sensitive detection are highly required.

[0020] As an example of an application of the diamond amplifier 20, for example, it can be incorporated into the amplifier unit 13 of a millimeter-wave band communication device 10 that uses millimeter-wave band (30-300 GHz) radio waves, as shown in Figure 2. Here, the millimeter-wave band communication device 10 includes a transmitting antenna 11 that transmits millimeter-wave band radio waves into space, a receiving antenna 12 that receives millimeter-wave band radio waves from space, an amplifier unit 13 that amplifies millimeter-wave band signals, a frequency converter 14 that converts between the millimeter-wave band and a frequency band that can be processed, and a signal processor 15 that processes signals at a processable frequency. The amplifier unit 13 includes a transmitting amplifier unit 13a that amplifies the millimeter-wave band signal from the frequency converter unit 14 and outputs it to the transmitting antenna 11, and a receiving amplifier unit 13b that amplifies the millimeter-wave band signal from the receiving antenna 12 and outputs it to the frequency converter unit 14. Each of the transmitting amplifier unit 13a and the receiving amplifier unit 13b incorporates a diamond amplifier 20 as shown in Figure 1.

[0021] The diamond transistor 30 is a transistor using a diamond semiconductor (see Figures 1 and 3). For example, a diamond field effect transistor (FET) can be used as the diamond transistor 30. Using a diamond FET offers advantages in terms of higher frequency, integration, and noise reduction. Among diamond FETs, using a diamond transistor using a hydrogen-terminated diamond semiconductor can achieve even higher performance (high frequency performance, high output performance, etc.). The diamond transistor 30 can be configured for use in environments with ionizing radiation doses of 50 μGy to 50 kGy / h (see Figure 16). The diamond transistor 30 can be configured for use in environments with temperatures of 100°C to 300°C (see Figure 15). While Figures 15 and 16 are not examples of the present application, they are reference data from which similar effects can be expected. The diamond transistor 30 can be a diamond FET, for example, a MESFET (Metal Semiconductor Field Effect Transistor) as shown in Figure 3, and can be configured to include a diamond semiconductor layer 32 having a hydrogen termination portion 32a, a source electrode 33a, a drain electrode 33b, and a gate electrode 35.

[0022] The diamond semiconductor layer 32 is a layer that includes diamond and a portion that functions as a semiconductor (see FIG. 3). The diamond semiconductor layer 32 can be formed, for example, by chemical vapor deposition of a diamond crystal (epitaxial diamond crystal) on a seed substrate using hydrogen and methane gas as raw materials using an MPCVD (Microwave Plasma Chemical Vapor Deposition) device, followed by removal of the seed substrate, resulting in a free-standing diamond film. The diamond semiconductor layer 32 thus formed has a hydrogen termination 32a on the (001) plane (upper surface). The hydrogen termination 32a has a hole channel formed therein and exhibits p-type conductivity. By subjecting the region of the hydrogen termination 32a other than the element region to ozone treatment to remove hydrogen, the hydrogen termination 32a can be configured to be present in the element region but not present in regions other than the element region. The portion of the diamond semiconductor layer 32 other than the hydrogen termination 32a is non-doped diamond. The configuration of the diamond semiconductor layer 32 on the diamond substrate 31 will be described later.

[0023] Here, the diamond semiconductor layer 32 having the hydrogen-terminated portion 32a boasts a transconductance approximately 10,000 times higher than that of the boron-doped diamond semiconductor layer 39 (boron concentration 10 ppm) in which diamond is doped with boron as in the comparative example of FIG. ｍａｘ High frequency characteristics of up to 120 GHz have also been confirmed. Therefore, by using a diamond transistor 30 including a diamond semiconductor layer 32 having a hydrogen termination 32a, it is possible to realize a high frequency amplification MMIC that operates in high frequency regions such as the millimeter wave band.

[0024] The source electrode 33a and the drain electrode 33b are electrodes made of a predetermined metal (e.g., Au) (see FIG. 3). The source electrode 33a and the drain electrode 33b are arranged on both sides of the channel region on the diamond semiconductor layer 32. In order to ensure adhesion with the diamond semiconductor layer 32, the source electrode 33a and the drain electrode 33b are preferably formed on the diamond semiconductor layer 32 in a state that has not been exposed to an etching agent, a resist stripper, or oxygen plasma for resist ashing. The source electrode 33a and the drain electrode 33b are preferably arranged so as to be in direct contact (ohmic contact) with the hydrogen termination portion 32a of the diamond semiconductor layer 32. The source electrode 33a and the drain electrode 33b can be formed, for example, by forming an Au film on the diamond semiconductor layer 32 (e.g., by vapor deposition or sputtering), forming a resist for forming the source electrode / drain electrode on the Au film, etching using the resist as a mask, and then removing the resist. The source electrode 33a and the drain electrode 33b can be configured, for example, by laminating metals such as Ti / Al / Ti on the diamond semiconductor layer 32, or by having a metal carbide layer (buffer layer) such as TiC at the interface between the lowest metal layer and the diamond semiconductor layer 32. The source / drain distance, which is the distance between the source electrode 33a and the drain electrode 33b, is preferably less than 500 nm, for example, when considering operation in a high frequency band (e.g., cutoff frequency 50 GHz to 100 GHz). The thicknesses of the source electrode 33a and the drain electrode 33b are preferably less than 100 nm when considering operation in a high frequency band, and are preferably less than 50 nm when considering obtaining desired RF (Radio Frequency) characteristics, and are preferably less than 25 nm when considering operation in an even higher frequency band (e.g., cutoff frequency over 100 GHz). The lower limit of the thickness of the source electrode 33a and the drain electrode 33b is the critical film thickness. The critical film thickness is the film thickness at which the desired function of each electrode can no longer be maintained, and in the diamond semiconductor of the present invention, it is, for example, several nm to 15 nm, preferably 10 nm or more.

[0025] The gate electrode 35 is an electrode disposed on the channel region of the hydrogen termination portion 32a of the diamond semiconductor layer 32 (see FIG. 3). The gate electrode 35 can be, for example, a metal film having a single layer structure of any of Al, Au, Ti, Mo, Cr, Ru, Cu, Pb, Zn, or Pt, or a laminate structure of any combination (e.g., Ti / Mo / Au, etc.). The thickness of the gate electrode 35 can be 10 nm to 500 nm. In a configuration having multiple diamond transistors, the thickness of the gate electrode 35 may be different from the viewpoint of process and device fabrication. The gate electrode 35 can be formed, for example, by forming a resist for gate electrode formation on the diamond semiconductor layer 32 (including the hydrogen termination portion 32a), using the resist as a mask to form a metal film for the gate electrode 35 on the diamond semiconductor layer 32 (e.g., by physical deposition methods such as sputtering or evaporation, or chemical deposition methods such as CVD or MOCVD), and then lifting off the resist and the metal film thereon.

[0026] The gate length of gate electrode 35 can be set within the following range of values ​​depending on the application of the high-frequency amplification MMIC. When the high-frequency amplification MMIC is applied to a communication system, a wireless LAN (Local Area Network), or a wireless communication device, the gate length of gate electrode 35 is preferably 1 μm to 10 μm, taking into account the required cutoff frequency of 500 MHz to 5 GHz. When the high-frequency amplification MMIC is applied to a millimeter-wave band communication device or a high-frequency sensing device, the gate length of gate electrode 35 is preferably 50 nm to 1 μm, taking into account the required cutoff frequency of 5 GHz to 100 GHz.

[0027] The diamond transistor 30 may be a MISFET (Metal Insulator Semiconductor Field Effect Transistor) as shown in Fig. 4, in addition to the MESFET shown in Fig. 3, and may have a configuration in which a gate insulating film 36 is interposed between the channel region of the hydrogen termination portion 32a of the diamond semiconductor layer 32 and the gate electrode 35. The gate insulating film 36 may be made of, for example, Al ２ O３ , SiO ２ , CaF ２ , HfO ２ , AlN, BN, Si ３ N ４ , SiON, Ta ２ O ５ , TiO ２ , WO ３ , LaF ３ , MgF ２ , YF ３ , Any single-layer structure of LiF or a laminated structure of any combination can be used as the insulating film. Instead of the gate insulating film 36, a space (air layer, vacuum layer, air gap) may be used. The gate insulating film 36 can be formed together with the gate electrode 35. For example, a resist for forming the gate electrode is formed on the diamond semiconductor layer 32 including the source electrode 33a and the drain electrode 33b, and using the resist as a mask, an insulating film for the gate insulating film 36 is formed by CVD method using a predetermined source gas. Subsequently, a metal film for the gate electrode 35 is formed on the gate insulating film 36 (for example, film formation by evaporation method, sputtering method, etc.). Then, the resist, and the insulating film and the metal film thereon are lifted off to form the gate insulating film 36 and the gate electrode 35.

[0028] 5, the diamond transistor 30 can be configured as a modified example of the MISFET shown in Fig. 4, in which the entire hydrogen termination portion 32a of the diamond semiconductor layer 32 between the source electrode 33a and the drain electrode 33b is covered with a gate insulating film 37. The gate insulating film 37 can be made of the same material (except for the space) as the gate insulating film 36. The gate insulating film 37 is formed in a separate process from the gate electrode 35. For example, a resist for forming the gate insulating film is formed on the diamond semiconductor layer 32, and an insulating film for the gate insulating film 37 is formed by a CVD method using a predetermined raw material gas using the resist as a mask, and then the resist and the insulating film thereon are lifted off, thereby forming the gate insulating film 37. In addition, the gate electrode 35 can be formed by, for example, forming a resist for gate electrode formation on the diamond semiconductor layer 32 including the source electrode 33a, the drain electrode 33b and the gate insulating film 37 after forming the gate insulating film 37, and then using the resist as a mask to form a metal film for the gate electrode 35 on the gate insulating film 37 (for example, by evaporation, sputtering, etc.), and then lifting off the resist and the metal film thereon. The purpose of covering the entire hydrogen termination 32a of the diamond semiconductor layer 32 between the source electrode 33a and the drain electrode 33b with the gate insulating film 37 is as follows. A problem specific to the diamond semiconductor layer 32 having the hydrogen termination 32a is that the conduction layer changes due to the hydrogen termination 32a. Since the hydrogen termination 32a, which becomes a channel near the surface of the diamond semiconductor layer 32, is easily affected by ions, etc., in order to stably exhibit excellent characteristics, a structure may be adopted in which the entire hydrogen termination 32a of the diamond semiconductor layer 32 between the source electrode 33a and the drain electrode 33b is protected.

[0029] 6, in order to obtain good ohmic contact between the source electrode 33a and the drain electrode 33b and the hydrogen termination portion 32a of the diamond semiconductor layer 32, contact portions 34a and 34b made of diamond semiconductor doped with P-type impurities may be provided between the source electrode 33a and the drain electrode 33b and the hydrogen termination portion 32a of the diamond semiconductor layer 32. When boron is used as the P-type impurity, the boron concentration of the contact portions 34a and 34b is, for example, 5×10 １９ / cm ３ ~1 x 10 ２２ / cm ３ The thickness of the contact portions 34a, 34b can be, for example, approximately 20 to 300 nm. When using boron as a P-type impurity, the contact portions 34a, 34b can be formed by forming a mask for forming the contact portions 34a, 34b on the diamond semiconductor layer 32 (including the hydrogen-terminated portion 32a), and then using an MPCVD apparatus to chemically vapor-deposit a P-type impurity-doped diamond semiconductor on the diamond semiconductor layer 32 using hydrogen, methane gas, and boron (trimethylboron) as raw materials (synthesis gas), followed by removing the metal mask. Using an MPCVD apparatus enables more precise control of conditions and uniform synthesis. Temperature control involves measuring the diamond temperature during synthesis with a radiation thermometer and providing real-time feedback to keep the temperature within a 5% error range of the synthesis target temperature, thereby reducing temperature variation during synthesis. Impurity input control involves supplying a high-quality boron source gas while controlling it with a high-precision mass flow meter, thereby minimizing variation in the boron concentration. The B / C ratio in the synthesis gas can be set to about 1.5 to 1.6%. Since diamond is difficult to ion-implant, when forming the ohmic contact portions 34a, 34b, it is desirable to form them separately from the formation of the source electrode 33a and the drain electrode 33b.

[0030] In addition, in the diamond transistor 30, in order to improve the adhesion between the source electrode 33a, the drain electrode 33b, and the gate electrode 35 (including the gate insulating film 36 if present) and the diamond semiconductor layer 32 and to further demonstrate the excellent characteristics of the high frequency amplification MMIC, the entire element can be covered with a passivation film 38 as shown in Fig. 7. In the passivation film 38, contact holes (not shown) leading to the source electrode 33a, the drain electrode 33b, and the gate electrode 35 are formed at positions different from the positions of the cross section in Fig. 7. The passivation film 38 can be made of, for example, Al ２ O ３ , SiO ２ , HfO ２ , AlN, BN, Si ３ N ４ , SiON, Ta ２ O ５ , TiO ２ , W.O. ３ , CaF ２ , LaF ３ , MgF ２ , Y.F. ３ Insulating films having a single layer structure of any of polyimide, epoxy resin, and acrylic resin or a laminated structure of any combination thereof can be used. In consideration of improving carrier mobility and processability, insulating materials containing F (fluorine), such as CaF ２ , LaF ３ , MgF ２Any one of the above or any combination thereof can be used. The passivation film 38 preferably covers and protects at least the entire channel region to prevent deterioration of electrical characteristics due to components such as ions, electrons, and radicals in the atmosphere. The thickness of the passivation film 38 is preferably 100 nm or more, taking into consideration the contact between the gate electrode 35 and the diamond semiconductor layer 32, and the contact between the source electrode 33 a and the drain electrode 33 b and the diamond semiconductor layer 32, and is preferably 300 nm or more, taking into consideration the flatness or flattening processability of the upper surface of the passivation film 38. The passivation film 38 is preferably made of a different material from the gate insulating film 36 in order to optimize the overall device characteristics. The dielectric constant of the passivation film 38 is preferably less than 15 F / m.

[0031] Furthermore, as shown in FIG. 8 , the diamond transistor 30 can be configured using a diamond substrate 31 as a support for the diamond transistor 30. The diamond substrate 31 is a substrate made of a diamond single crystal. For example, a high-temperature, high-pressure synthetic diamond single crystal substrate can be used as the diamond substrate 31. For example, the diamond substrate 31 preferably uses the (001) plane of the diamond substrate 31 and has an off-angle of 3 degrees. In order to reduce variations in the amount of impurities incorporated during the deposition of the diamond semiconductor layer 32, the diamond substrate 31 is preferably polished, for example, before the deposition of the diamond semiconductor layer 32, to a surface roughness Ra (arithmetic mean roughness) of less than 5 nm, more preferably less than 1 nm. In order to reduce changes in resistance value due to defects in the diamond semiconductor layer 32, it is preferable to remove polishing defects from the diamond substrate 31 by ion beam etching, for example, before the deposition of the diamond semiconductor layer 32. In order to suppress abnormal growth of the diamond semiconductor layer 32, it is preferable to thoroughly remove organic and inorganic substances from the surface of the diamond substrate 31 by, for example, washing with strong acid in a clean room before forming the diamond semiconductor layer 32. This can reduce variations in the resistance value of the diamond semiconductor layer 32.

[0032] When used in a high frequency amplification MMIC, the thickness of the diamond substrate 31 is preferably 50 μm to 450 μm, more preferably 50 μm to 250 μm, taking into consideration heat dissipation and handling.

[0033] Here, in a configuration with a high-frequency amplifier MMIC capable of high-frequency, high-power operation on a diamond substrate, assuming a thermal conductivity of the diamond substrate of 20 W / cm·K, an ambient temperature of 20°C, and a loss of 20 W in the amplifier section, the inventors simulated the amplifier section temperature of the high-frequency amplifier MMIC by varying the thickness of the diamond substrate. The following analysis was obtained. Although the diamond substrate has very high thermal conductivity, heat dissipation can naturally become an issue during high-power operation. The thicker the diamond substrate, the higher the amplifier section temperature (see Figure 13). Considering the adverse effects on peripheral components of the amplifier section, it is generally best to keep the amplifier section temperature below 100°C. However, depending on the design and the use of high-temperature circuit components, it is possible to tolerate temperatures around 120°C. However, due to the unique characteristics of diamond, the small substrate size makes it difficult to implement the automated processes refined in the semiconductor industry. Therefore, manual processing and device assembly are required, and due to the substrate's fragility, the diamond substrate 31 should be at least 50 μm thick. From the above, in a configuration having a high frequency amplification MMIC on a diamond substrate, the thickness of the diamond substrate 31 is preferably 50 μm to 450 μm, more preferably 50 μm to 250 μm, taking into consideration heat dissipation and handling.

[0034] In addition, in a configuration with a high-frequency amplifier MMIC capable of high-frequency, high-power operation on substrates with various thermal conductivities, the ambient temperature was set to 20°C, the substrate thickness was set to 250 μm, and a loss of 8 W was assumed in the amplifier section. The inventors conducted a simulation of the amplifier section temperature of the high-frequency amplifier MMIC mounted on the substrate. The following analysis was obtained: A GaN substrate with a thermal conductivity of 2.3 W / cm·K easily exceeded 100°C, which is considered undesirable for practical use of circuit components and transistors (see Figure 13). Therefore, increasing the output power of a high-frequency amplifier MMIC requires increasing the size of the transistors and adding a new heat dissipation mechanism (see Figure 13). On the other hand, a diamond substrate with a thermal conductivity of 20 W / cm·K only had an element temperature of about 30°C, demonstrating excellent heat dissipation due to its overwhelming thermal conductivity. Incidentally, the diamond semiconductor used in diamond transistors is an ultra-wide bandgap semiconductor, allowing diamond transistors to operate at temperatures as high as 500°C. Therefore, by combining appropriate high-temperature circuit components (for example, high-temperature resistor elements), it is possible to configure a high-frequency amplification MMIC even in an ambient environment ranging from room temperature to 300°C or below, particularly in a high-temperature environment of 100°C to 300°C.

[0035] According to form 1, the diamond amplifier 20 is constructed using a diamond transistor 30 having a diamond semiconductor layer 32 with a hydrogen termination portion 32a, which can contribute to improving performance (high temperature performance, high voltage resistance performance, high frequency performance, high output performance, etc.) while reducing the process and miniaturizing the device.

[0036] Furthermore, according to the first aspect, by constructing a high-frequency amplification MMIC on the diamond substrate 31, it is possible to fabricate a small, lightweight, and high-performance device even including a matching circuit, thereby saving mounting space and improving space efficiency in various systems such as radar systems and communication systems. Furthermore, by using an MMIC, it is possible to reduce manufacturing costs.

[0037] Furthermore, according to form 1, the configuration utilizes the overwhelming physical properties of diamond, making it possible to operate in environments (under high temperatures, high voltages, radiation, etc.) that are impossible with existing materials (silicon, GaN, etc.).

[0038] Furthermore, according to the first embodiment, the diamond semiconductor layer 32 has the highest thermal conductivity among semiconductors, and therefore has excellent heat dissipation properties, and can operate at high output even in high temperature environments of 50° C. or higher.

[0039] Furthermore, according to the first embodiment, the diamond semiconductor layer 32 having a high breakdown field strength is used, so that the reliability of operation under high voltage can be improved.

[0040] Furthermore, according to form 1, diamond transistor 30 is used, which has high carrier mobility and saturated drift velocity, and a low dielectric constant, and can therefore contribute to improving the performance of high-frequency devices in a wide range of applications, including not only mobile base stations but also various radar equipment and satellite communications. In fact, the performance index of the device is much higher than that of other materials; for example, the Johnson figure of merit, which is the performance index of high-frequency, high-power devices, of diamond is 1,100 times that of silicon and more than twice that of GaN, which is known as a next-generation semiconductor.

[0041] Furthermore, according to the first aspect, since the diamond transistor 30, which has excellent pressure resistance and thermal conductivity, is used, even if the device dimensions are reduced to increase the frequency, the influence of deterioration in the pressure resistance characteristics can be minimized, and it becomes possible to realize MMICs on a scale that was not possible with existing material devices. Note that several next-generation semiconductor materials, such as GaN, have been proposed to overcome the pressure resistance problem that was a problem with silicon, but in actual operation, heat dissipation becomes a bottleneck, making it difficult to reduce the device size.

[0042] Furthermore, according to the first aspect, the amplifier circuit 22 is configured to include matching circuits 21 and 23 for impedance matching between the receiving side and the sending side, thereby enabling highly efficient operation. Furthermore, by implementing an MMIC including the matching circuits 21 and 23, a high gain and a low noise level can be obtained, allowing for accurate amplification and transmission of high-frequency signals, and enabling the overall amplifier to be made smaller, more efficient, and operate at higher frequencies.

[0043] Furthermore, according to the first aspect, the diamond transistor 30, which has excellent radiation resistance, is used, enabling stable and long-term operation in radiation environments such as space and nuclear environments. This enables stable operation for a long period of time in high-radiation environments such as space and nuclear power plants, and can also be incorporated into space exploration equipment and the control systems of nuclear facilities. In radiation environments where only very limited amplifiers have been used until now, it is now possible to select a small, high-output, high-frequency amplifier MMIC that can operate at high frequencies, which is a significant advantage when building a system.

[0044] [Form 2] A diamond amplifier according to Form 2 will be described with reference to the drawings. Fig. 14 shows (A) a block diagram schematically illustrating an example of the configuration of a diamond amplifier according to Form 2, and (B) a cross-sectional view schematically illustrating an example of the configuration of a diamond transistor in the diamond amplifier.

[0045] The diamond amplifier 20 comprises an amplifier circuit 22 including at least one diamond transistor 30 having a source electrode 33a, a drain electrode 33b, and a gate electrode 35 arranged on a diamond semiconductor layer 32, and one or both of an input matching circuit connected to the input side of the amplifier circuit 22 and an output matching circuit connected to the output side of the amplifier circuit 22, namely, matching circuits 21, 23.

[0046] According to form 2, the diamond amplifier 20 is constructed using a diamond transistor 30 having a diamond semiconductor layer 32, which contributes to improving performance (high temperature performance, high voltage resistance performance, high frequency performance, high output performance, etc.) while reducing the process and miniaturizing the device.

[0047] Some or all of the above aspects may be described as, but are not limited to, the following supplementary notes.

[0048] [Appendix 1] A diamond amplifier comprising: an amplifier circuit including at least one diamond transistor having a source electrode, a drain electrode, and a gate electrode arranged on a diamond semiconductor layer; and one or both of an input matching circuit connected to the input side of the amplifier circuit and an output matching circuit connected to the output side of the amplifier circuit. [Appendix 2] A diamond amplifier according to Appendix 1, comprising a diamond substrate on which the amplifier circuit and the matching circuit are mounted. [Appendix 3] A diamond amplifier according to Appendix 1 or 2, wherein the impedance of the matching circuit is 1 Ω to 100 Ω. [Appendix 4] A diamond amplifier according to Appendix 1 or 2, wherein the impedance of the matching circuit is 45 Ω to 55 Ω. [Appendix 5] A diamond amplifier according to any one of Appendixes 1 to 4, wherein the diamond semiconductor layer has a hydrogen termination on the (001) plane. [Appendix 6] A diamond amplifier according to any one of Appendixes 1 to 5, wherein the diamond transistor is a MESFET in which the gate electrode is arranged directly on the diamond semiconductor layer. [Supplementary Note 7] The diamond amplifier according to any one of Supplementary Note 1 to Supplementary Note 5, wherein the diamond transistor is a MISFET having a gate insulating film disposed between the gate electrode and the diamond semiconductor layer. [Supplementary Note 8] The gate insulating film is Al ２ O ３ , SiO ２ , CaF ２ , HfO ２ , AlN, BN, Si ３ N ４ , SiON, Ta ２ O ５ , TiO ２ , W.O. ３ , LaF ３ , MgF ２ , Y.F. ３ , LiF, LaF ３The diamond amplifier according to Supplementary Note 7, wherein the gate insulating film is an insulating film made of a single layer structure of any one of the above or a laminated structure of any combination thereof. [Supplementary Note 9] The gate insulating film covers the entire diamond semiconductor layer between the source electrode and the drain electrode. The diamond amplifier according to Supplementary Note 7 or 8. [Supplementary Note 10] The diamond amplifier according to any one of Supplementary Notes 1 to 9, wherein the gate electrode has a gate length of 50 nm to 10 μm. [Supplementary Note 11] The diamond amplifier according to any one of Supplementary Notes 1 to 10, comprising a passivation film covering the entire diamond semiconductor layer including the source electrode, the drain electrode and the gate electrode. [Supplementary Note 12] The passivation film is made of Al ２ O ３ , SiO ２ , HfO ２ , AlN, BN, Si ３ N ４ , SiON, Ta ２ O ５ , TiO ２ , W.O. ３ , CaF ２ , LaF ３ , MgF ２ , Y.F. ３, polyimide, epoxy resin, and acrylic resin, or a laminated structure of any combination thereof. [Appendix 13] The diamond amplifier according to any one of Appendices 7 to 9, comprising a passivation film covering the entire diamond semiconductor layer including the source electrode, the drain electrode, and the gate electrode, the passivation film being made of a material different from the material of the gate insulating film. [Appendix 14] The diamond amplifier according to any one of Appendices 1 to 13, comprising a P-type impurity-doped diamond semiconductor layer disposed between the source electrode and the drain electrode and the diamond semiconductor layer. [Appendix 15] The diamond amplifier according to any one of Appendices 1 to 14, which is used in an environment where the ionizing radiation dose is 50 μGy / h to 50 kGy / h. [Appendix 16] The diamond amplifier according to any one of Appendices 1 to 15, which is used in an environment where the temperature is from room temperature to 300°C or less, or from 100°C to 300°C. [Supplementary Note 17] The diamond amplifier according to any one of Supplementary Notes 1 to 16, wherein the frequency of the input signal is 500 MHz to 100 GHz. [Supplementary Note 18] An electric machine or device comprising the diamond amplifier according to any one of Supplementary Notes 1 to 17.

[0049] The disclosures of the above-cited patent documents are incorporated herein by reference and may be used as the basis or part of the present invention, as necessary. Modifications and adjustments of the embodiments and examples are possible within the scope of the entire disclosure of the present invention (including the claims and drawings), and further based on the basic technical concepts thereof. Furthermore, various combinations and selections (or non-selections, as necessary) of the various disclosed elements (including each element of each claim, each element of each embodiment or example, each element of each drawing, etc.) are possible within the scope of the entire disclosure of the present invention. In other words, the present invention naturally includes various modifications and alterations that would be possible by a person skilled in the art in accordance with the entire disclosure and technical concepts, including the claims and drawings. Furthermore, with regard to the numerical values ​​and numerical ranges described in this application, any intermediate values, lower values, and smaller ranges are deemed to be included, even if not explicitly stated. Furthermore, the disclosures of the above-cited documents, when used in part or in whole in combination with the disclosures herein as part of the disclosure of the present invention, are also deemed to be included in (belong to) the disclosures of this application, in accordance with the spirit of the present invention.

[0050] REFERENCE SIGNS LIST 10 Millimeter wave band communication device 11 Transmitting antenna 12 Receiving antenna 13 Amplifying section 13a Transmitting amplifier section 13b Receiving amplifier section 14 Frequency conversion section 15 Signal processing section 20, 20a, 20b Diamond amplifier 21 Input matching circuit (matching circuit) 22 Amplifying circuit 23 Output matching circuit (matching circuit) 30 Diamond transistor 31 Diamond substrate 32 Diamond semiconductor layer 32a Hydrogen termination section 33a Source electrode 33b Drain electrode 34a, 34b Contact section 35 Gate electrode 36, 37 Gate insulating film 38 Passivation film 39 Boron-doped diamond semiconductor layer

Claims

1. A diamond amplifier comprising: an amplifier circuit including at least one diamond transistor having a source electrode, a drain electrode, and a gate electrode arranged on a diamond semiconductor layer; and one or both of an input matching circuit connected to the input side of the amplifier circuit and an output matching circuit connected to the output side of the amplifier circuit.

2. The diamond amplifier according to claim 1, comprising a diamond substrate on which the amplifier circuit and the matching circuit are mounted.

3. The diamond amplifier according to claim 1 or 2, wherein the diamond semiconductor layer has a hydrogen termination on the (001) plane.

4. A diamond amplifier according to any one of claims 1 to 3, wherein the diamond transistor is a MESFET in which the gate electrode is disposed directly on the diamond semiconductor layer.

5. A diamond amplifier according to any one of claims 1 to 3, wherein the diamond transistor is a MISFET in which a gate insulating film is disposed between the gate electrode and the diamond semiconductor layer.

6. The gate insulating film is Al ２ O ３ , SiO ２ , CaF ２ , HfO ２ , AlN, BN, Si ３ N ４ , SiON, Ta ２ O ５ , TiO ２ , W.O. ３ , LaF ３ , MgF ２ , Y.F. ３ , LiF, LaF ３ The diamond amplifier according to claim 3, wherein the insulating film is made of a single layer structure of any one of the above or a laminated structure of any combination thereof.

7. A diamond amplifier according to claim 5 or 6, wherein the gate insulating film covers the entire diamond semiconductor layer between the source electrode and the drain electrode.

8. A diamond amplifier according to any one of claims 1 to 7, comprising a passivation film that covers the entire diamond semiconductor layer including the source electrode, the drain electrode, and the gate electrode.

9. The passivation film is Al ２ O ３ , SiO ２ , HfO ２ , AlN, BN, Si ３ N ４ , SiON, Ta ２ O ５ , TiO ２ , W.O. ３ , CaF ２ , LaF ３ , MgF ２ , Y.F. ３ 9. The diamond amplifier according to claim 8, wherein the insulating film is made of a single layer structure of any one of polyimide, epoxy resin, and acrylic resin, or a laminate structure of any combination thereof.

10. A diamond amplifier according to any one of claims 5 to 7, comprising a passivation film covering the entire diamond semiconductor layer including the source electrode, the drain electrode, and the gate electrode, the material of the passivation film being different from the material of the gate insulating film.

11. A diamond amplifier according to any one of claims 1 to 10, comprising a P-type impurity doped diamond semiconductor layer disposed between the source electrode, the drain electrode and the diamond semiconductor layer.

12. A diamond amplifier according to any one of claims 1 to 11, which is used in an environment where the amount of ionizing radiation is 50 μGy / h to 50 kGy / h.

13. A diamond amplifier according to any one of claims 1 to 12, which is used in an environment where the temperature is 300°C or less or 100°C to 300°C.

14. An electrical appliance comprising a diamond amplifier according to any one of claims 1 to 13.

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