Discrete gate-based gallium nitride HEMT device with low reverse threshold voltage

Abstract

The invention discloses a low reverse threshold voltage gallium nitride HEMT (High Electron Mobility Transistor) device based on a discrete gate. The device comprises an epitaxial layer of a convex structure or a stepped structure; wherein the protruding part of the epitaxial layer, namely the upper table top, is called an active region, the upper surface of the active region is provided with a source electrode, a top gate electrode and a drain electrode, the source electrode and the drain electrode are located at the two ends of the upper surface of the active region respectively, and the top gate electrode is located between the source electrode and the drain electrode; one or more discrete side gate electrodes are arranged on the upper surface of the lower table top of the epitaxial layer of the stepped structure, and one or more discrete side gate electrodes are arranged on the upper surfaces of the lower table tops on the two sides of the epitaxial layer of the convex structure respectively. According to the GaN HEMT power electronic device, the discrete side gate electrode structure is introduced, so that the device realizes lower reverse conduction threshold voltage under the condition that the forward threshold voltage is not reduced, and the GaN HEMT power electronic device can be used for solving the problems of overlarge dead time loss and the like when the GaN HEMT power electronic device works reversely.

Description

Technical Field

[0001] The present invention relates to the field of GaN HEMT devices in the field of semiconductor technology, and in particular to a GaN HEMT device structure with low reverse threshold voltage based on discrete gate technology. Background Art

[0002] GaN, or gallium nitride, is a semiconductor material with wide bandgap characteristics. Compared with the widely used traditional silicon material, GaN has better electron mobility and saturation velocity, as well as a wider bandgap width. These unique properties make GaN perform well in high frequency, high voltage and high temperature environments, while also demonstrating excellent current carrying capacity and low forward conduction loss. Due to the lack of a body diode and the coupling relationship between the forward and reverse threshold voltages, the traditional GaN HEMT has a higher threshold voltage when reverse-conducting, sometimes even exceeding its forward-conducting threshold voltage, which leads to excessive dead-time power consumption. By cleverly designing GaN HEMT devices, the reverse-conducting threshold voltage can be reduced without sacrificing the forward-conducting threshold voltage, thereby solving the inherent problem of excessive reverse conduction losses.

[0003] GaN HEMT devices with low reverse conduction threshold voltage are an innovative technology in the field of power electronics. They combine the design advantages of the freewheeling diode structure and conventional HEMT transistors, remove the parallel configuration of the freewheeling diode in a limited space, and achieve low reverse conduction voltage operation. Such devices are very suitable for demanding applications, such as power management systems for electric vehicles, inverters for renewable energy systems, power supplies for high-performance computing and data centers, and RF amplifiers for communication base stations.

[0004] In the prior art, there is a GaN RC-HEMT (CN113675270A) with reverse conduction capability. This patent introduces a current blocking layer and a multi-channel conductive path based on the traditional MIS gate HEMT device, and integrates a reverse freewheeling Schottky tube. The blocking layer forms a 2DHG to block the longitudinal current path, realizing the device enhancement type. When forward conduction occurs, the gate increases the potential, and the gate sidewall forms an inversion layer to conduct the longitudinal channel. The multi-channel conductive path in the drift region and the electron accumulation layer formed under the gate both reduce the on-resistance; when forward blocking occurs, the blocking layer assists in modulating the electric field in the depleted drift region and reduces the electric field spike. The polarization electric field formed in the multi-channel region can further increase the withstand voltage of the drift region, effectively alleviating the contradictory relationship between the on-resistance and the withstand voltage; when reverse freewheeling occurs, the integrated Schottky tube forms a current path along the 2DEG to reduce the conduction loss.

[0005] However, the above-mentioned prior art process is complicated to implement and integrates other structures including SBD and PN junction, resulting in low device space utilization. Since Schottky diodes are used, they are subject to the limitation of the turn-on voltage of Schottky diodes. Summary of the invention

[0006] The core goal of the present invention is to improve the problem of dead time loss caused by excessively high reverse threshold voltage in GaN HEMT devices. Based on the existing GaN HEMT devices, we propose a new type of gallium nitride HEMT device structure with low reverse conduction threshold voltage. While keeping the forward conduction threshold voltage unaffected, this structure changes the potential distribution of the channel by adding a discrete side gate, achieving a significant reduction in the reverse conduction threshold voltage and a larger reverse saturation current. This innovation even allows the device to be transformed from a normally-off type to a normally-on type in the reverse working state, greatly reducing the problem of excessive dead time loss in the device when working in reverse.

[0007] The purpose of the present invention is achieved by at least one of the following technical solutions.

[0008] A discrete-gate-based low reverse threshold voltage gallium nitride HEMT device includes an epitaxial layer with a convex structure or a stepped structure;

[0009] The protruding part of the epitaxial layer, i.e., the upper table, is called the active region. A source electrode, a top gate electrode, and a drain electrode are arranged on the upper surface of the active region. The source electrode and the drain electrode are located at two ends of the upper surface of the active region, respectively, and the top gate electrode is located between the source electrode and the drain electrode.

[0010] One or more discrete side gate electrodes are arranged on the upper surface of the lower mesa of the stepped structure epitaxial layer, and one or more discrete side gate electrodes are arranged on the upper surfaces of the lower mesas on both sides of the convex structure epitaxial layer.

[0011] Further, the epitaxial layer includes a substrate, a nucleation layer, a buffer layer, an insertion layer and a barrier layer stacked sequentially from bottom to top.

[0012] Furthermore, when a stepped epitaxial layer is used, one side of the epitaxial layer is etched to a depth exceeding the thickness of the barrier layer to form a stepped structure, and the protruding portion is the active area;

[0013] When an epitaxial layer with a convex structure is used, etching is performed on both sides of the epitaxial layer to a depth exceeding the thickness of the barrier layer to form a convex structure, and the convex portion is an active area.

[0014] Furthermore, the substrate in the epitaxial layer is a silicon carbide substrate or a silicon substrate, and the buffer layer and the barrier layer form a heterojunction with a polarization effect, including but not limited to gallium nitride / aluminum gallium nitride.

[0015] Furthermore, the source electrode and the drain electrode both adopt a multi-layer metal stack, which is Ti / Al / Ni / Au from bottom to top, with thicknesses of 20 / 100 / 10 / 100 nm respectively.

[0016] Furthermore, the top gate electrode and the discrete side gate electrodes are both made of a multi-layer metal stack, which is Ni / Au from bottom to top, with a thickness of 50 / 200 nm.

[0017] Furthermore, when a discrete side gate electrode is provided on the upper surface of the lower terrace of the stepped epitaxial layer or the upper surface of the lower terraces on both sides of the convex epitaxial layer, the center position of the discrete side gate electrode must be aligned with the center of the top gate electrode on the upper surface of the active area.

[0018] Furthermore, when multiple discrete side gate electrodes are arranged on the upper surface of the lower terrace of the epitaxial layer of the stepped structure, the multiple discrete side gate electrodes constitute a multi-side gate structure, and the center position of the multi-side gate structure must be exactly opposite to the center of the top gate electrode on the upper surface of the active area.

[0019] Furthermore, when multiple discrete side gate electrodes are arranged on the upper surface of the lower table on both sides of the epitaxial layer of the convex structure, the multiple discrete side gate electrodes arranged on the upper surface of the lower table on the same side constitute a multi-side gate structure, and the center positions of the multi-side gate structures on both sides must be directly opposite to the center of the top gate electrode on the upper surface of the active area.

[0020] Further, the cross-section of the discrete side gate electrode includes a rectangle, a triangle or a trapezoid.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] 1. The present invention introduces a discrete side-gate electrode structure, so that the reverse conduction turn-on voltage of the device is lower than that of the traditional HEMT without reducing the forward threshold voltage, thereby achieving lower reverse conduction loss.

[0023] 2. The reverse saturation current of this device is larger than that of conventional devices, which is more conducive to working as a reverse device

[0024] 3. In terms of process implementation, the process steps are simpler than conventional gate separation devices.

[0025] 4. Compared with the conduction mode of the freewheeling diode in parallel with the external circuit, this new structure solves this problem from the source and greatly saves costs.

[0026] 5. Schottky diode is not used, and it is not limited by the turn-on voltage of parallel Schottky diode or PN junction diode technology. When working in reverse, a lower turn-on voltage can be achieved, and even the normally closed type can be transformed into a normally open type. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a diagram of an epitaxial layer structure in an embodiment of the present invention;

[0028] Figure 2 is a structural diagram of a conventional HEMT device in an embodiment of the present invention;

[0029] Figure 3 It is a schematic structural diagram of a gallium nitride HEMT device with a low reverse conduction threshold voltage in an embodiment of the present invention;

[0030] Figure 4 for Figure 3 A cross-sectional view of a GaN HEMT device with a low reverse conduction threshold voltage;

[0031] Figure 5 It is a schematic structural diagram of a gallium nitride HEMT device with a low reverse conduction threshold voltage in an embodiment of the present invention;

[0032] Figure 6 It is a schematic structural diagram of a gallium nitride HEMT device with a low reverse conduction threshold voltage in an embodiment of the present invention;

[0033] Figure 7 It is a transfer characteristic curve diagram of the gallium nitride HEMT device with low reverse conduction threshold voltage in the embodiment of the present invention and the conventional HEMT device in the forward conduction state and the reverse conduction state under rectangular coordinates;

[0034] Figure 8 Graph showing transfer characteristics of a gallium nitride HEMT device with a low reverse conduction threshold voltage and a conventional HEMT device in a logarithmic coordinate system in a forward conduction state and a reverse conduction state in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following description combines specific illustrations to explain the technical solution so as to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and similar generalized embodiments made by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0036] The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this specification. The singular forms of "a", "the" and "the" used in one or more embodiments of this specification and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in one or more embodiments of this specification refers to and includes any or all possible combinations of one or more associated listed items.

[0037] It should be understood that although the terms first, second, etc. may be used to describe various information in one or more embodiments of this specification, this information should not be limited to these terms. These terms are only used to distinguish similar objects and are not necessarily used to describe the order or sequence of features described in one or more embodiments of this specification. In addition, the terms "having" and "including" are similarly expressed to indicate a non-exclusive scope. For example, a process, method, system, product or device that includes a series of steps or modules is not necessarily limited to the contents listed in detail, but may include inherent contents related to these steps or modules that are not listed.

[0038] Example:

[0039] Conventional HEMT device structure is as follows Figure 2 As shown, it includes an epitaxial layer 1, the upper part of the epitaxial layer 1 is an active area 2, and a source electrode 3, a top gate electrode 4 and a drain electrode 5 are arranged on the upper surface of the active area 2. The source electrode 3 and the drain electrode 5 are respectively located at the two ends of the upper surface of the active area 2, and the top gate electrode 4 is located between the source electrode 3 and the drain electrode 5.

[0040] A discrete gate based low reverse threshold voltage GaN HEMT device, such as Figure 3 As shown, an epitaxial layer 1 including a stepped structure;

[0041] The protruding portion of the epitaxial layer 1, i.e., the upper table, is called the active region 2. A source electrode 3, a top gate electrode 4, and a drain electrode 5 are arranged on the upper surface of the active region 2. The source electrode 3 and the drain electrode 5 are located at two ends of the upper surface of the active region 2, respectively, and the top gate electrode 4 is located between the source electrode 3 and the drain electrode 5.

[0042] like Figure 3 , Figure 4 and Figure 6 As shown, one or more discrete side gate electrodes 6 are provided on the upper surface of the lower terrace of the epitaxial layer 1 of the stepped structure.

[0043] like Figure 1 As shown, the epitaxial layer 1 includes a substrate, a nucleation layer, a buffer layer, an insertion layer and a barrier layer stacked in sequence from bottom to top.

[0044] In one embodiment, Figure 3 As shown, when a stepped structure epitaxial layer 1 is used, one side of the epitaxial layer 1 is etched to a depth exceeding the thickness of the barrier layer to form a stepped structure, and the protruding portion is the active region 2;

[0045] In one embodiment, the substrate in the epitaxial layer 1 is a silicon substrate, and the heterojunction with polarization effect formed by the buffer layer and the barrier layer is specifically aluminum gallium nitride.

[0046] In one embodiment, the source electrode 3 and the drain electrode 5 are both made of a multi-layer metal stack, which is Ti / Al / Ni / Au from bottom to top, with thicknesses of 20 / 100 / 10 / 100 nm, respectively.

[0047] In one embodiment, the top gate electrode 4 and the discrete side gate electrode 6 are both made of a multi-layer metal stack, which is Ni / Au from bottom to top, with a thickness of 50 / 200 nm.

[0048] In one embodiment, Figure 3 As shown, when a discrete side gate electrode 6 is disposed on the upper surface of the lower terrace of the stepped epitaxial layer 1 , the center position of the discrete side gate electrode 6 must be aligned with the center of the top gate electrode 4 on the upper surface of the active region 2 .

[0049] In one embodiment, Figure 6 As shown, when multiple discrete side gate electrodes 6 are arranged on the upper surface of the lower table of the stepped epitaxial layer 1, the multiple discrete side gate electrodes 6 constitute a multi-side gate structure, and the center position of the multi-side gate structure must be exactly opposite to the center of the top gate electrode 4 on the upper surface of the active area 2.

[0050] In one embodiment, a discrete gate based low reverse threshold voltage GaN HEMT device, such as Figure 5 As shown, an epitaxial layer 1 including a convex structure;

[0051] The protruding portion of the epitaxial layer 1, i.e., the upper table, is called the active region 2. A source electrode 3, a top gate electrode 4, and a drain electrode 5 are arranged on the upper surface of the active region 2. The source electrode 3 and the drain electrode 5 are located at two ends of the upper surface of the active region 2, respectively, and the top gate electrode 4 is located between the source electrode 3 and the drain electrode 5.

[0052] like Figure 6 As shown, one or more discrete side gate electrodes 6 are respectively disposed on the upper surfaces of the lower terraces on both sides of the epitaxial layer 1 of the convex structure.

[0053] like Figure 1 As shown, the epitaxial layer 1 includes a substrate, a nucleation layer, a buffer layer, an insertion layer and a barrier layer stacked in sequence from bottom to top.

[0054] In one embodiment, Figure 5 As shown, when a convex structure epitaxial layer 1 is used, both sides of the epitaxial layer 1 are etched to a depth exceeding the thickness of the barrier layer to form a convex structure, and the protruding portion is the active area 2.

[0055] In one embodiment, the substrate in the epitaxial layer 1 is a silicon carbide substrate, and the heterojunction with polarization effect formed by the buffer layer and the barrier layer is specifically gallium nitride.

[0056] In one embodiment, the source electrode 3 and the drain electrode 5 are both made of a multi-layer metal stack, which is Ti / Al / Ni / Au from bottom to top, with thicknesses of 20 / 100 / 10 / 100 nm, respectively.

[0057] In one embodiment, the top gate electrode 4 and the discrete side gate electrode 6 are both made of a multi-layer metal stack, which is Ni / Au from bottom to top, with a thickness of 50 / 200 nm.

[0058] In one embodiment, as shown in FIG5 , when a discrete side gate electrode 6 is disposed on the upper surface of the lower terraces on both sides of the epitaxial layer 1 of the convex structure, the center position of the discrete side gate electrode 6 needs to be aligned with the center of the top gate electrode 4 on the upper surface of the active area 2 .

[0059] In one embodiment, when multiple discrete side gate electrodes 6 are arranged on the upper surface of the lower table on both sides of the epitaxial layer 1 of the convex structure, the multiple discrete side gate electrodes 6 arranged on the upper surface of the lower table on the same side constitute a multi-side gate structure, and the center positions of the multi-side gate structures on both sides must be directly opposite to the center of the top gate electrode 4 on the upper surface of the active area 2.

[0060] In one embodiment, three discrete side gate electrodes 6 are disposed on the upper surface of the lower mesa on one side of the epitaxial layer 1 of the convex structure, and two discrete side gate electrodes 6 are disposed on the upper surface of the lower mesa on the other side.

[0061] In one embodiment, the cross-section of the discrete side gate electrode 6 is rectangular.

[0062] In one embodiment, the cross-section of the discrete side gate electrode 6 is triangular.

[0063] In one embodiment, the cross-section of the discrete side gate electrode 6 is trapezoidal.

[0064] In one embodiment, Figure 7 and Figure 8 As shown, a schematic diagram comparing the transfer characteristics of the forward conduction state and the reverse conduction state of a gallium nitride HEMT device with a low reverse conduction threshold voltage and a conventional HEMT device is shown, wherein: Figure 7 is the transfer characteristic curve under rectangular coordinates, Figure 8 It is the transfer characteristic curve under logarithmic coordinates.

[0065] In the Silvaco simulation example, Figure 7 and Figure 8The transfer characteristic curves of the forward conduction state and the reverse conduction state of the HEMT device of the present invention are compared with those of the conventional HEMT device. It can be seen from the curves that the device of the present invention can significantly reduce the reverse conduction threshold voltage (so that the forward and reverse threshold voltages are separated) while keeping the forward conduction threshold voltage basically unchanged (the reverse threshold voltage has a decrease of about 0.25V, when the electrode bias is 4V), while the forward and reverse threshold voltages of the conventional HEMT are consistent, and the transfer characteristic curves under logarithmic coordinates are almost overlapped. In addition, the reverse conduction saturation current of the device of the present invention is very large. The superior characteristics of the device of the present invention are of great significance for device realization and reducing reverse conduction dead zone loss.

[0066] The device can significantly reduce the reverse conduction threshold voltage while keeping the forward conduction threshold voltage basically unchanged, and the reverse turn-on threshold voltage will significantly decrease as the reverse bias voltage of the device increases, and can even be normally open. This superior characteristic is of great significance for reducing reverse dead zone losses.

[0067] The above embodiments are only preferred examples of the present invention and do not constitute any limitation to the present invention. It is obvious that for professionals in this field, after understanding the content and principles of the present invention, they can make various modifications and changes in form and details according to the method of the present invention without departing from the principles and scope of the present invention. However, these modifications and changes based on the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A discrete gate based low reverse threshold voltage gallium nitride HEMT device, characterized in that: An epitaxial layer (1) comprising a convex structure or a stepped structure; The protruding portion of the epitaxial layer (1), i.e., the upper table, is called the active region (2). A source electrode (3), a top gate electrode (4), and a drain electrode (5) are arranged on the upper surface of the active region (2). The source electrode (3) and the drain electrode (5) are respectively located at two ends of the upper surface of the active region (2), and the top gate electrode (4) is located between the source electrode (3) and the drain electrode (5). One or more discrete side gate electrodes (6) are arranged on the upper surface of the lower table of the epitaxial layer (1) of the stepped structure, and one or more discrete side gate electrodes (6) are arranged on the upper surfaces of the lower tables on both sides of the epitaxial layer (1) of the convex structure.

2. A discrete gate based low reverse threshold voltage gallium nitride HEMT device according to claim 1, characterized in that: The epitaxial layer (1) comprises a substrate, a nucleation layer, a buffer layer, an insertion layer and a barrier layer which are stacked in sequence from bottom to top.

3. The discrete gate based low reverse threshold voltage gallium nitride HEMT device according to claim 2, characterized in that: When a stepped epitaxial layer (1) is used, one side of the epitaxial layer (1) is etched to a depth exceeding the thickness of the barrier layer to form a stepped structure, and the protruding portion is the active region (2); When a convex-structured epitaxial layer (1) is used, both sides of the epitaxial layer (1) are etched to a depth exceeding the thickness of the barrier layer to form a convex structure, and the convex portion is an active region (2).

4. The discrete gate based low reverse threshold voltage gallium nitride HEMT device according to claim 2, characterized in that: The substrate in the epitaxial layer (1) is a silicon carbide substrate or a silicon substrate, and the buffer layer and the barrier layer form a heterojunction with a polarization effect, including but not limited to gallium nitride / aluminum gallium nitride.

5. The discrete gate based low reverse threshold voltage gallium nitride HEMT device according to claim 1, characterized in that: The source electrode (3) and the drain electrode (5) are both made of multi-layer metal stacks, which are Ti / Al / Ni / Au from bottom to top, with thicknesses of 20 / 100 / 10 / 100 nm respectively.

6. The discrete gate based low reverse threshold voltage gallium nitride HEMT device according to claim 1, characterized in that: The top gate electrode (4) and the discrete side gate electrode (6) both adopt a multi-layer metal stack, which is Ni / Au from bottom to top, with a thickness of 50 / 200 nm.

7. The discrete gate based low reverse threshold voltage gallium nitride HEMT device according to claim 1, characterized in that: When a discrete side gate electrode (6) is provided on the upper surface of the lower table of the epitaxial layer (1) of the stepped structure, or on the upper surface of the lower table on both sides of the epitaxial layer (1) of the convex structure, the center position of the discrete side gate electrode (6) must be directly opposite to the center of the top gate electrode (4) on the upper surface of the active area (2).

8. The GaN HEMT structure with low reverse threshold voltage based on discrete gate technology according to claim 1, characterized in that: When a plurality of discrete side gate electrodes (6) are arranged on the upper surface of the lower table of the stepped epitaxial layer (1), the plurality of discrete side gate electrodes (6) form a multi-side gate structure, and the center position of the multi-side gate structure needs to be exactly opposite to the center of the top gate electrode (4) on the upper surface of the active region (2).

9. The GaN HEMT structure with low reverse threshold voltage based on discrete gate technology according to claim 1, characterized in that: When a plurality of discrete side gate electrodes (6) are arranged on the upper surfaces of the lower terraces on both sides of the epitaxial layer (1) of the convex structure, the plurality of discrete side gate electrodes (6) arranged on the upper surface of the lower terrace on the same side form a multi-side gate structure, and the center positions of the multi-side gate structures on both sides must be exactly opposite to the center of the top gate electrode (4) on the upper surface of the active region (2).

10. The GaN HEMT structure with low reverse threshold voltage based on discrete gate technology according to claim 1, characterized in that: The cross-section of the discrete side gate electrode (6) includes a rectangle, a triangle or a trapezoid.

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