A highly linear GaN HEMT RF power device

Abstract

The present invention discloses a high-linearity GaN HEMT radio frequency power device, comprising a substrate layer, a buffer layer, a channel layer, a barrier layer, and a protective layer, arranged in sequence. A source electrode, a gate electrode, and a drain electrode are disposed above the protective layer. The protective layer forms an L-shaped groove, and the source electrode is disposed at the top of the L-shaped groove, so that the source and gate electrodes are horizontally staggered. By adopting the technical solution of the present invention, the protective layer is formed into an L-shaped groove, which vertically elevates the source electrode until the bottom of the source electrode is flush with the top of the gate electrode, thereby fundamentally eliminating the presence of Cgs. As the output power increases, Cgs no longer affects the change in the Δ value, thereby alleviating the tendency of the Δ value to move away from zero and effectively improving the device linearity.

Description

Technical Field

[0001] The present invention belongs to the field of radio frequency power devices, and in particular relates to a high-linearity GaN HEMT radio frequency power device. Background Art

[0002] With the continuous development of wireless communication technology, communication systems have evolved from the initial 1G network era to the current 5G network era. With the improvement of data transmission rate and spectrum utilization, more complex modulation methods have been widely used, such as orthogonal frequency division multiplexing and orthogonal amplitude modulation, which make the signal have a higher peak-to-average ratio. This puts higher requirements on the linearity of the RF power amplifier, the most core circuit in the communication system. Generally speaking, the linearity of the RF power amplifier is mainly determined by the linearity of the RF power device.

[0003] GaN HEMT RF power devices are widely used in various communication systems with high linearity performance due to their high breakdown voltage, high saturation speed and outstanding thermal properties. Figure 1 , shown is a cross-sectional view of an existing GaN HEMT RF power device, where Drain is the drain port, Gate is the gate port, Source is the source port, Si3N4 is the dielectric material between the gate, drain, and source, GaN cap is the device protection layer, AlGaN barrier layer is a barrier layer that confines free electrons to move in the two-dimensional electron gas, GaN channel is a channel layer with a high free electron concentration, GaN buffer is the buffer layer, and Substrate is the device substrate. Its basic operating principle is that when the Drain, Gate, and Source are connected to appropriate voltages, free electrons are transmitted from the Source port to the Drain port through the two-dimensional electron gas, and the signal enters the Gate port and is output at the Drain port, achieving signal amplification. The distortion during signal amplification is considered the linearity performance of the device. However, existing GaN HEMT RF power devices have significant shortcomings in linearity performance, which directly limits their further application in certain communication systems that require high linearity performance.

[0004] Therefore, in view of the defects of the existing technology, it is necessary to propose a technical solution to solve the technical problems existing in the existing technology. Summary of the Invention

[0005] In view of this, it is indeed necessary to provide a highly linear GaN HEMT RF power device. The protective layer is made into an L-shaped groove, so that the source port is raised in the vertical direction so that the bottom of the Source port is flush with the top of the Gate port, thereby fundamentally eliminating the existence of Cgs. As the output power increases, Cgs no longer affects the change of the Δ value, thereby alleviating the trend of the Δ value away from 0 and effectively improving the linearity of the device.

[0006] In order to solve the technical problems existing in the prior art, the technical solutions of the present invention are as follows:

[0007] A high-linearity GaN HEMT radio frequency power device includes a substrate layer, a buffer layer, a channel layer, a barrier layer, and a protective layer arranged in sequence, with a source electrode, a gate electrode, and a drain electrode arranged above the protective layer. The protective layer forms an L-shaped groove, and the source electrode is arranged at the top of the L-shaped groove so that the source end and the gate end are staggered in horizontal space.

[0008] As a further improvement, the top of the drain port is flush with the top of the gate port, and the bottom of the source port is flush with the top of the gate port.

[0009] As a further improvement, the channel layer uses GaN material.

[0010] As a further improvement, the barrier layer is made of AlGaN material.

[0011] As a further improvement, the substrate layer is made of SiC material.

[0012] As a further improvement, the buffer layer uses GaN material.

[0013] As a further improvement, Si3N4 dielectric material is filled between the source, gate, and drain. Dielectrics are required to isolate ports within semiconductor devices. Si3N4 has strong oxidation resistance, can withstand thermal shock, offers high insulation properties, and is relatively inexpensive to manufacture. This makes it ideal for use as an isolation dielectric in semiconductor devices, and is used in all GaN HEMT devices.

[0014] Compared with the prior art, the present invention changes the structure of the protective layer so that the Source port and the Gate port are staggered in the horizontal space, thereby fundamentally eliminating the existence of Cgs. This means that when Δ increases with the output power, Cgs no longer affects the change of Δ value, thereby alleviating the trend of Δ value away from 0 and effectively improving the linearity of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a structural cross-sectional diagram of a conventional GaN HEMT radio frequency power device.

[0016] Figure 2 A cross-sectional view of the structure of a high-linearity GaN HEMT RF power device.

[0017] In the figure, Drain is the drain port, Gate is the gate port, Source is the source port, Si3N4 is the dielectric material between the gate, drain and source, GaN cap is the device protection layer of the L-shaped groove structure, AlGaN barrier layer is the blocking layer that limits the free electrons to move on the two-dimensional electron gas, GaN channel is the channel layer with a high free electron concentration, GaN buffer is the buffer layer, and Substrate is the substrate of the device.

[0018] Figure 3 This is a structural block diagram of another preferred embodiment of the present invention.

[0019] In the figure, the AlGaN barrier layer and AlGaN extra layer are barrier layers that restrict free electrons from moving in the two-dimensional electron gas, and are respectively marked as the first barrier layer and the second barrier layer. The area between the AlGaN barrier layer and the GaN channel is the original first two-dimensional electron gas, and the area between the GaN channel and the AlGaN extra layer is the newly formed second two-dimensional electron gas.

[0020] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0021] The technical solution provided by the present invention will be further described below with reference to the accompanying drawings.

[0022] Currently, all GaN HEMT devices have a planar structure, meaning the source, drain, and gate terminals are flush. However, this type of GaN HEMT RF power device suffers from significant linearity issues, primarily due to the presence of gate-source parasitic capacitance. This parasitic capacitance increases squarely with increasing output power, causing Δ to drift further and further away from zero as output power increases, significantly degrading linearity.

[0023] To this end, the present invention first deduces from the circuit level. The applicant found that the linearity performance of GaN HEMT RF power devices can also be expressed as the change in gain with output power Δ. The closer Δ is to 0, the better the linearity performance, and the further Δ is from 0, the worse the linearity performance. Δ can be expressed as the following formula:

[0024]

[0025] Where K is a constant, gm is the transconductance of the power device, Cgs is the parasitic capacitance from Gate to Source, s is the frequency response (Once the operating frequency is determined, S is a constant), and Pout is the output power of the power device.

[0026] For GaN HEMT RF power devices, the metal on the Gate port and the metal on the Source port are horizontally close to each other, and the space between them is filled with Si3N4 dielectric. This leads to the existence of gate-source parasitic capacitance Cgs, which increases at the square of the Pout. This causes Δ to move further away from zero as the output power increases, significantly deteriorating linearity performance. This is one of the main reasons why GaN HEMT RF power devices have significant linearity defects.

[0027] Based on the above theoretical analysis, the present invention proposes a high linearity GaN HEMT RF power device, see Figure 2 , shown is a structural block diagram of the GaN HEMT RF power device, including a substrate layer, a buffer layer, a channel layer, a barrier layer, and a protective layer arranged in sequence, with a source electrode, a gate electrode, and a drain electrode arranged above the protective layer; wherein the protective layer forms an L-shaped groove, and the source electrode is arranged at the top of the L-shaped groove so that the source end and the gate end are staggered with each other in the horizontal space.

[0028] The above technical solution etches the GaN cap layer into an L-shaped groove structure, and then metallizes the top of the L-shaped groove to form a Source port. The bottom of the Source port is flush with the top of the Gate port. At this time, the metal on the Gate will be completely staggered with the metal on the Source, fundamentally eliminating the existence of Cgs, thereby alleviating the trend of Δ away from 0 as the output power increases, and effectively improving the linearity of the device.

[0029] Furthermore, the applicant has also found in the research that the variation law of the transconductance gm of the power device is specifically shown in the following formula (2).

[0030]

[0031] As the output power increases from a small signal to saturation power, the voltage swings on the gate and drain continue to increase, which means |VGS| + |VDS| continues to increase. Furthermore, the increase in |VGS| causes electrons in the two-dimensional electron gas to be continuously drawn into the gate, causing N(x) to decrease. Ultimately, gm decreases with increasing output power, causing Δ to move further away from zero as output power increases, significantly deteriorating linearity performance. This is one of the main reasons why GaN HEMT RF power devices have significant linearity drawbacks.

[0032] To this end, based on the above technical solution, the applicant has made further improvements. Figure 3 , shown is a structural block diagram of another preferred embodiment of the device. The GaN HEMT RF power device includes a substrate layer, a buffer layer, a second barrier layer (AlGaN extra layer), a channel layer (GaN channel layer), a first barrier layer (AlGaN barrier layer), and a protective layer, which are arranged in sequence. The protective layer forms an L-shaped groove so that the source terminal and the gate terminal are staggered in horizontal space. A first two-dimensional electron gas and a second two-dimensional electron gas are formed between the channel layer and the first and second barrier layers. The source, gate, and drain are used to receive external control signals to control the electron movement of the first and second two-dimensional electron gases formed in the channel layer.

[0033] In the above technical solution, applying power to the gate generates an electric field perpendicular to the 2D electron gas. As the electric field on the gate gradually strengthens, electrons in the first 2D electron gas will escape from it and reach the gate, causing electron loss. When the electric field increases to a certain level, the electron loss in the original 2D electron gas will cease. After the introduction of the AlGaN extra layer, the electrons in the newly formed second 2D electron gas will also be affected by the electric field and move toward the gate. In this process, some electrons will move into the original first 2D electron gas, thus compensating for the electron loss in the original 2D electron gas. In other words, when the signal is large, electrons in the second 2D electron gas will flow into the first 2D electron gas.

[0034] Compared to traditional structures, the present invention adds an AlGaN extra layer beneath the GaN channel layer, ultimately forming a GaN channel layer, an AlGaN extra layer, and an AlGaN barrier layer. The thickness of the AlGaNext layer and the AlGaN barrier layer remains the same. The GaN channel layer cannot be too thick, otherwise the second two-dimensional electron gas cannot enter the first two-dimensional electron gas. Its thickness is typically around 100 nanometers. The electrons in the second two-dimensional electron gas formed by the GaN channel layer and the AlGaN extra layer can effectively compensate for the loss of electrons in the original two-dimensional electron gas, alleviating the decrease in gm and, in turn, the tendency of the Δ value to move away from zero, effectively improving the linearity of the device.

[0035] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0036] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-linearity GaN HEMT radio frequency power device, characterized in that: The device comprises a substrate layer, a buffer layer, a channel layer, a barrier layer, and a protective layer, wherein a source electrode, a gate electrode, and a drain electrode are arranged on top of the protective layer; wherein the protective layer forms an L-shaped groove, and the source electrode is arranged at the top of the L-shaped groove so that the source electrode port and the gate electrode port are staggered with each other in the horizontal space; the top of the drain port is flush with the top of the gate port, and the bottom of the source port is flush with the top of the gate port; the channel layer is made of GaN material; and the barrier layer is made of AlGaN material.

2. The high-linearity GaN HEMT radio frequency power device according to claim 1, characterized in that: The substrate layer is made of SiC material.

3. The high-linearity GaN HEMT radio frequency power device according to claim 1, characterized in that: The buffer layer is made of GaN material.

4. The high-linearity GaN HEMT radio frequency power device according to claim 1, characterized in that: Si3N4 dielectric material is filled between the source, gate and drain.

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