An n-channel HEMT depletion mode device having a comb-finger field plate structure

Abstract

This invention belongs to the field of semiconductor power device technology and provides an n-channel HEMT depletion-type device with a comb-finger field plate structure to solve the problem of large parasitic capacitance introduced by the field plate structure in the prior art affecting the dynamic performance of the device. This invention employs a comb-finger field plate structure between the gate and drain of the gallium nitride HEMT device, while simultaneously etching the AlGaN barrier layer beneath the comb-finger field plate and filling it with insulating filler. During forward conduction, a two-dimensional electron gas is formed between the unetched AlGaN barrier layer and the GaN buffer layer, serving as a conductive channel. During reverse breakdown, the drift region channel forms a large-area depletion region under the modulation effect of the comb-finger field plate, improving the device's breakdown voltage performance. Furthermore, the comb-finger field plate and the channel have almost no overlap in the vertical direction, significantly reducing the parasitic capacitance introduced by the field plate, enabling the device to maintain good breakdown voltage characteristics while also possessing superior high-frequency characteristics.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor power device technology, specifically providing an n-channel HEMT depletion-type device with a comb-finger field plate structure. Background Technology

[0002] Currently, power electronics technology has permeated all aspects of social production and life. Power devices, as the core for converting and controlling electrical energy, are one of the key technologies in power electronics. With the continuous development of power device technology, the performance of traditional silicon-based semiconductor devices is gradually encountering bottlenecks when entering applications such as millimeter waves, high temperatures, and high power. Gallium nitride (GaN), a third-generation wide-bandgap semiconductor material, has broad application prospects in the field of high-frequency, high-power, and high-efficiency power electronic devices due to its large bandgap, strong breakdown electric field, high electron saturation drift velocity, and excellent high-temperature resistance. Among them, the high electron mobility transistor (HEMT) is currently the most widely used GaN power and radio frequency device.

[0003] As GaN HEMTs develop towards higher voltage withstand and higher power, the devices are prone to generating high electric field concentration on the drain side when turned off, which can lead to breakdown, increased leakage current, or reliability degradation. Therefore, improving the voltage withstand capability of devices has become an important research direction in current GaN HEMT technology. Field plate technology is currently the mainstream method for adjusting the electric field distribution in the device channel to improve the device's voltage withstand. The field plate is usually a metal electrode that is insulated from the semiconductor layer by a dielectric layer and extends spatially to cover the channel outside the gate or above the drain drift region. By connecting the field plate to the gate, source, or drain potential, the potential distribution in the channel region can be readjusted when the device is turned off. Field plates can be classified into gate field plates, source field plates, drain field plates, and floating field plates according to the different connected electrodes. In existing GaN HEMT devices, field plate structures are widely used to reduce the peak electric field between the gate and drain and improve the turn-off breakdown voltage. However, field plates often introduce significant parasitic capacitance, which sacrifices dynamic performance while improving the device's breakdown voltage, thus limiting further improvement in the overall device performance. Therefore, how to effectively control the electric field distribution and improve the device's breakdown voltage performance without excessively sacrificing the device's dynamic performance has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide an n-channel HEMT depletion-type device with a comb-finger field plate structure to solve the problem of large parasitic capacitance introduced by the field plate structure affecting the dynamic performance of gallium nitride n-channel HEMT depletion-type power devices. At the same time, the device also has good reverse breakdown voltage performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An n-channel HEMT depletion-type device with a comb-finger field plate structure includes: a substrate (1), a buffer layer (2) disposed on the upper surface of the substrate (1), a barrier layer (3) disposed on the upper surface of the buffer layer (2), and a gate (4), a source (5) and a drain (6) disposed on the upper surface of the barrier layer (3).

[0007] The feature is that a heterojunction is formed at the contact interface between the buffer layer (2) and the barrier layer (3), and a two-dimensional electron gas is provided at the heterojunction interface as a conductive channel (7); the source (5) and drain (6) are disposed on both sides of the upper surface of the barrier layer (3) and form an ohmic contact with the conductive channel (7); the gate (4) is disposed between the source (5) and drain (6) on the upper surface of the barrier layer (3) and forms a Schottky contact with the barrier layer (3); the barrier layer (3) is etched to form a comb-like shape, with gaps (8) between the combs. The inner barrier layer material is completely etched away and filled with insulating filler (9); the barrier layer (3) between the gate (4) and the drain (6) and the upper surface of the insulating filler (9) are covered with an insulating medium (10); multiple strip metal field plates (11) arranged in a comb-finger pattern are provided on the upper surface of the insulating medium (10), so that the strip metal field plates and the comb-finger gaps (8) are arranged one-to-one; the strip metal field plates (11) do not contact the source (5) and the drain (6), and are electrically connected to the gate (4).

[0008] Furthermore, each strip of metal field plate does not completely or partially cover the insulating medium (10) in the area directly above the comb-shaped barrier layer (3).

[0009] Furthermore, the insulating filler layer (9) and the insulating medium (10) may use the same material or different material.

[0010] Furthermore, the metal field plate (11) is chamfered at the end near the drain side to suppress electric field concentration.

[0011] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0012] This invention provides an n-channel HEMT depletion-type device with a comb-finger field plate structure. In terms of its working principle:

[0013] This invention involves etching the barrier layer of a gallium nitride (GaN) device to form comb-finger-shaped voids and filling them with insulating filler. Due to the spontaneous polarization and piezoelectric polarization effects of GaN material, a high concentration of two-dimensional electron gas will be generated at the AlGaN / GaN heterojunction interface in the unetched region of the GaN HEMT device, forming a conductive channel. When the device is reverse-biased, the comb-finger-shaped metal field plate connected to the gate will deplete the two-dimensional electron gas in the channel, as shown in the depletion region. Figure 9 As shown. Figure 10 As shown, as the drain negative voltage increases further, the two-dimensional electron gas under the unetched barrier layer will be gradually and completely depleted, generating a large-area depletion region. The channel is blocked over a large area, thus forming a breakdown voltage region, thereby ensuring the breakdown voltage performance of the device.

[0014] Conventional field plate structures, while improving device withstand voltage, introduce significant parasitic capacitance, typically viewed as a parallel-plate capacitor formed between the field plate and the channel. In contrast, in this invention, the barrier layer beneath the comb-finger field plate is etched, and the comb-finger field plate and the channel do not have a large overlap area in the vertical direction. Figure 2 As shown, this can significantly reduce the parasitic capacitance introduced by the field plate structure and ensure good high-frequency characteristics of the device.

[0015] In summary, this invention employs a comb-finger field plate structure between the gate and drain of a GaN HEMT device, and etches and fills the barrier layer below the comb-finger field plate with insulating filler. This ensures good forward conduction characteristics and reverse withstand voltage performance of the device while reducing the parasitic capacitance introduced by the field plate structure, thereby realizing a high-voltage GaN HEMT device with good high-frequency characteristics. Attached Figure Description

[0016] Figure 1 This is a three-dimensional structural diagram of an n-channel HEMT depletion-type device with a comb-finger field plate structure according to the present invention.

[0017] Figure 2 This is a schematic diagram of the cross-sectional structure A of the n-channel HEMT depletion-type device with a comb-finger field plate structure in this invention, perpendicular to the current direction.

[0018] Figure 3 This is a schematic diagram of the three-dimensional structure of the GaN buffer layer formed on the upper surface of the substrate in an embodiment of the present invention.

[0019] Figure 4 This is a schematic diagram of the three-dimensional structure of the AlGaN barrier layer formed on the GaN buffer layer in an embodiment of the present invention.

[0020] Figure 5 This is a schematic diagram of a three-dimensional structure of a source and drain electrode formed with an ohmic contact with a GaN buffer layer on the upper surface of an AlGaN barrier layer in an embodiment of the present invention.

[0021] Figure 6 This is a schematic diagram of a three-dimensional structure of a gate forming a Schottky contact with the AlGaN barrier layer on the upper surface of the AlGaN barrier layer in an embodiment of the present invention.

[0022] Figure 7 This is a schematic diagram of a comb-like void three-dimensional structure obtained by etching the AlGaN barrier layer in an embodiment of the present invention.

[0023] Figure 8 This is a three-dimensional structural diagram of an insulating filler filling the gaps in an embodiment of the present invention.

[0024] Figure 9 This is a schematic diagram of the depletion region in an n-channel HEMT depletion-type device with a comb-finger field plate structure under low voltage, as described in an embodiment of the present invention.

[0025] Figure 10 This is a schematic diagram showing that the depletion region of an n-channel HEMT depletion-type device with a comb-finger field plate structure is completely depleted under high voltage in an embodiment of the present invention.

[0026] In the above figures, 1 is the substrate, 2 is the buffer layer, 3 is the barrier layer, 4 is the gate, 5 is the source, 6 is the drain, 7 is the conductive channel, 8 is the interdigital gap, 9 is the insulating filler, 10 is the insulating dielectric layer, and 11 is the metal field plate. Detailed Implementation

[0027] To enable those skilled in the art to better understand the purpose, technical solution, and principles of this invention, a detailed description is provided below in conjunction with the accompanying drawings and embodiments. The content of this invention is not limited to any specific embodiment, nor does it represent the best embodiment; common substitutions well-known to those skilled in the art are also covered within the scope of protection of this invention.

[0028] This embodiment provides an n-channel HEMT depletion-type device with a comb-finger gate field plate structure, the structure of which is as follows: Figure 1 and Figure 2 As shown, it specifically includes: a substrate (1), a buffer layer (2) disposed on the upper surface of the substrate (1), a barrier layer (3) disposed on the upper surface of the buffer layer (2), and a gate (4), a source (5) and a drain (6) disposed on the upper surface of the barrier layer (3).

[0029] A heterojunction is formed at the contact interface between the buffer layer (2) and the barrier layer (3), and a two-dimensional electron gas is provided at the heterojunction interface as a conductive channel (7); the source (5) and drain (6) are disposed on both sides of the upper surface of the barrier layer (3) and form an ohmic contact with the conductive channel (7); the gate (4) is disposed between the source (5) and drain (6) and forms a Schottky contact with the barrier layer (3) to regulate the conduction state of the conductive channel (7);

[0030] The barrier layer (3) is etched to form a comb-like shape. The barrier layer material in the gaps (8) between the combs is completely etched away and filled by an insulating filling layer (9). An insulating medium (10) covers the upper surface of the barrier layer (3) and the insulating filling layer (9) between the gate (4) and the drain (6). Multiple strip metal field plates (11) arranged in a comb-like pattern are set on the upper surface of the insulating medium (10), so that a strip metal field plate is set directly above each comb-like gap (8), and each strip metal field plate does not completely cover or does not completely cover the insulating medium (10) in the area directly above the comb-like barrier layer (3). The metal field plate (11) does not contact the source (5) and drain (6), but is electrically connected to the gate (4). Since the comb-like metal field plate (11) does not have a large overlap area with the conductive channel (9) in the vertical direction, the capacitance between the metal field plate (11) and the conductive channel (7) will be significantly reduced.

[0031] The working process of the above-mentioned HEMT device is explained in detail below:

[0032] The present invention provides a comb-shaped field plate structure on the insulating medium (10) between the gate and the drain, and etches the barrier layer below the comb-shaped metal field plate (11) and fills it with insulating filler (9).

[0033] When the gate (4) is not subjected to a positive voltage that turns on the conductive channel (7), the two-dimensional electron gas at the heterojunction interface formed by the barrier layer (3) and the buffer layer (2) is depleted, the conductive channel (7) is in the off state, and the device exhibits off characteristics. When the device is off and the drain (6) is subjected to a high negative voltage, the metal field plate (11) at the same position as the gate (4) has a depletion effect on the two-dimensional electron gas of the conductive channel (7) between the gate and drain. The edge of the channel will be depleted to form a depletion region. As the negative voltage of the drain (6) increases, the conductive channel (7) is completely depleted, and the depletion region will serve as a withstand voltage region to withstand high voltage.

[0034] When a forward voltage is applied to the gate (4) to make the device meet the conduction conditions, a two-dimensional electron gas will be generated at the heterojunction interface formed by the unetched area in the barrier layer (3) and the buffer layer (2). The two-dimensional electron gas forms a conductive channel (7) between the source (5) and the drain (6). Since the unetched barrier layer area is uniformly distributed in the plane, the formed two-dimensional electron gas ensures that the device has good forward conduction characteristics on a macroscopic level.

[0035] Since the barrier layer (3) under the metal field plate (11) is etched to form a gap (8) and filled with insulating filler (9), there is almost no overlap between the metal field plate (11) and the conductive channel (7), which significantly reduces the parasitic capacitance introduced by the metal field plate (11) and reduces the negative impact on the high-frequency characteristics of the device.

[0036] Furthermore, such as Figures 3 to 8 As shown, a method for fabricating an n-channel HEMT depletion-type device with a comb-finger gate field plate structure is presented. This embodiment uses the fabrication process of a GaN-based n-channel HEMT device, which includes the following steps:

[0037] Step 1: Grow a GaN buffer layer (2) on the substrate (1), as follows Figure 3 As shown;

[0038] Step 2: An AlGaN barrier layer (3) is grown on the GaN buffer layer (2), and a heterojunction is formed at the interface between the GaN buffer layer (2) and the AlGaN barrier layer (3), thereby generating a two-dimensional electron gas at the interface of the heterojunction. The two-dimensional electron gas constitutes a conductive channel (7), as shown in Figure 4.

[0039] Step 3: Mesa etching is performed on the epitaxial structure to form the active region of the device. Subsequently, source (5) and drain (6) are fabricated on the mesa surface, and ohmic contacts are formed between the source (5) and drain (6) and the conductive channel (7) through processes such as annealing. Figure 5 As shown;

[0040] Step 4: Fabricate a gate (4) above the AlGaN barrier layer (3) to form a Schottky contact between the gate (4) and the AlGaN barrier layer (3) to control the conduction state of the conductive channel (7), such as... Figure 6 As shown;

[0041] Step 5: In a predetermined region between the gate (4) and the drain (6), the AlGaN barrier layer (3) is patterned and etched to form multiple gaps (8) arranged in a comb-like pattern, such as... Figure 7 As shown;

[0042] Step 6: Deposit insulating filler (9) in the voids (8), such as Figure 8 As shown;

[0043] Step 7: An insulating dielectric (10) is deposited on the barrier layer (3) between the gate (4) and the drain (6), and a metal field plate (11) is fabricated on the insulating dielectric (10). The metal field plate (11) is etched by photolithography and etching processes so that the metal field plate (11) is arranged in a comb-like pattern and is arranged vertically above the gap (8) left by the etching of the barrier layer (3). At the same time, the metal field plate (11) is electrically connected to the gate (4) of the device, thereby forming a surface withstand voltage structure for controlling the electric field distribution between the gate (4) and the drain (6). The subsequent processes are consistent with the existing HEMT fabrication process, and finally the GaN-based HEMT device of this embodiment is obtained, as shown in the figure. Figure 1 As shown.

[0044] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. An n-channel HEMT depletion-type device with a comb-finger field plate structure, comprising: Substrate (1), buffer layer (2) disposed on the upper surface of substrate (1), barrier layer (3) disposed on the upper surface of buffer layer (2), gate (4), source (5), drain (6) disposed on the upper surface of barrier layer (3), and a voltage-resistant structure composed of metal field plate (11) and insulating dielectric (10) and (9) disposed in the region between gate (4) and drain (6); The feature is that a heterojunction is formed at the contact interface between the buffer layer (2) and the barrier layer (3), and a two-dimensional electron gas is provided at the interface of the heterojunction as a conductive channel (7); the source (5) and drain (6) are disposed on both sides of the upper surface of the barrier layer (3) and form an ohmic contact with the conductive channel (7); the gate (4) is disposed between the source (5) and drain (6) on the upper surface of the barrier layer (3) and forms a Schottky contact with the barrier layer (3); a portion of the barrier layer (3) between the gate (4) and drain (6) is etched to form a comb-like shape. The barrier layer material in the gap (8) between the fingers is completely etched away and filled with insulating filler (9); the barrier layer (3) between the gate (4) and the drain (6) and the upper surface of the insulating filler (9) are covered with an insulating medium (10); multiple strip metal field plates (11) arranged in a comb-like pattern are provided on the upper surface of the insulating medium (10), so that the strip metal field plates are arranged directly opposite the gap (8) between the fingers; the strip metal field plates (11) do not contact the source (5) and the drain (6), and are electrically connected to the gate (4).

2. The n-channel HEMT depletion-type device with a comb-finger field plate structure according to claim 1, characterized in that, Each strip of metal field plate is either completely or partially covered by the insulating medium (10) directly above the comb-shaped barrier layer (3).

3. The n-channel HEMT depletion-type device with a comb-finger field plate structure according to claim 1, characterized in that, The insulating filler layer (9) and the insulating medium (10) may use the same material or different material.

4. The n-channel HEMT depletion-type device with a comb-finger field plate structure according to claim 1, characterized in that, The metal field plate (11) is chamfered at the end near the drain side to suppress electric field concentration.

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