A low reverse threshold voltage gallium nitride HEMT device based on discrete gate
By introducing a discrete side-gate structure into GaN HEMT devices, the channel potential distribution is changed, which solves the problem of excessive reverse threshold voltage, achieves low reverse conduction loss and large reverse saturation current, simplifies the process and reduces costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTH CHINA UNIV OF TECH
- Filing Date
- 2024-11-29
- Publication Date
- 2026-05-22
AI Technical Summary
Existing GaN HEMT devices suffer from dead time loss due to excessively high reverse threshold voltage, and the existing processes are complex and have low space utilization.
Gallium nitride HEMT devices employing discrete side-gate structures can change the channel potential distribution by setting discrete side-gate electrodes on the epitaxial layer, thereby reducing the reverse conduction threshold voltage and converting to normally open mode in reverse operation.
Without affecting the forward conduction threshold voltage, it significantly reduces reverse conduction loss, increases reverse saturation current, has a simple process, low cost, avoids the limitations of Schottky diodes, and achieves normally open switching.
Smart Images
Figure CN119630025B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of GaN HEMT devices in the semiconductor technology field, and particularly to a gallium nitride HEMT device structure with low reverse threshold voltage based on discrete gate technology. Background Technology
[0002] Gallium nitride (GaN) is a semiconductor material with a wide bandgap. Compared to widely used traditional silicon, GaN exhibits superior electron mobility and saturation velocity, as well as a wider bandgap. These unique properties enable GaN to perform exceptionally well in high-frequency, high-voltage, and high-temperature environments, while also demonstrating excellent current carrying capacity and low forward conduction losses. Traditional GaN HEMTs lack a body diode, and a coupling relationship exists between the forward and reverse threshold voltages, resulting in a high threshold voltage during reverse conduction, sometimes even exceeding the forward conduction threshold voltage. This leads to excessively high dead-time power consumption. Through clever design of GaN HEMT devices, the reverse conduction threshold voltage can be reduced without sacrificing the forward conduction threshold voltage, thus solving the inherent problem of excessively high reverse conduction losses.
[0003] GaN HEMT devices with low reverse conduction threshold voltage represent an innovative technology in power electronics. They combine the design advantages of freewheeling diode structures and conventional HEMT transistors, eliminating the need for parallel freewheeling diodes within a limited space to achieve low reverse conduction voltage operation. These devices are ideally suited 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 on the basis of traditional MIS gate HEMT devices, and integrates a reverse freewheeling Schottky diode. The blocking layer forms a 2DHG to block the longitudinal current path, realizing the enhancement mode of the device. When forward conduction is performed, a high potential is applied to the gate, and an inversion layer is formed on the gate sidewall 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 is performed, the blocking layer assists in depleting the drift region to modulate the electric field, reducing the electric field spike. The polarization electric field formed in the multi-channel region can further improve the breakdown voltage of the drift region, effectively alleviating the contradiction between on-resistance and breakdown voltage. When reverse freewheeling is performed, the integrated Schottky diode forms a current path along the 2DEG, reducing conduction loss.
[0005] However, the aforementioned existing technologies are complex to implement and integrate other structures including SBD and PN junction, resulting in low device space utilization. Furthermore, due to the use of Schottky diodes, they are subject to the limitations of the Schottky diode's turn-on voltage. Summary of the Invention
[0006] The core objective of this invention is to improve the dead-time loss problem caused by excessively high reverse threshold voltage in GaN HEMT devices. Based on existing GaN HEMT devices, we propose a novel gallium nitride HEMT device structure with low reverse conduction threshold voltage. This structure, while maintaining the forward conduction threshold voltage unaffected, alters the channel potential distribution by adding discrete side gates, achieving a significant reduction in reverse conduction threshold voltage and a larger reverse saturation current. This innovation even allows the device to switch from normally off to normally on in reverse operation, greatly reducing the problem of excessive dead-time loss during reverse operation.
[0007] The objective of this invention is achieved by at least one of the following technical solutions.
[0008] A gallium nitride HEMT device with low reverse threshold voltage based on discrete gate, comprising an epitaxial layer with a convex or stepped structure;
[0009] The protruding part of the epitaxial layer, namely the upper platform, is called the active region. The active region is provided with an active electrode, a top gate electrode, and a drain electrode on its upper surface. 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.
[0010] One or more discrete side gate electrodes are provided on the upper surface of the lower stage of the stepped epitaxial layer, and one or more discrete side gate electrodes are provided on the upper surface of the lower stage on both sides of the convex epitaxial layer.
[0011] Furthermore, the epitaxial layer comprises a substrate, a nucleation layer, a buffer layer, an insertion layer, and a barrier layer stacked sequentially from bottom to top.
[0012] Furthermore, when using a stepped epitaxial layer, one side of the epitaxial layer is etched to a depth exceeding the thickness of the barrier layer to form a stepped structure, with the protruding part being the active region.
[0013] When using an epitaxial layer with a convex structure, 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, with the protruding part being the active region.
[0014] Furthermore, the substrate in the epitaxial layer is a silicon carbide substrate or a silicon substrate, and the heterojunction with polarization effect formed by the buffer layer and the barrier layer includes, but is not limited to, gallium nitride / aluminum gallium nitride.
[0015] Furthermore, both the source and drain electrodes employ multilayer metal stacks, consisting of Ti / Al / Ni / Au from bottom to top, with thicknesses of 20 / 100 / 10 / 100 nm, respectively.
[0016] Furthermore, both the top gate electrode and the discrete side gate electrode are made of multilayer metal stacks, with Ni / Au layers from bottom to top, and thicknesses of 50 / 200nm.
[0017] Furthermore, when a discrete side gate electrode is disposed on the upper surface of the lower platform of the stepped epitaxial layer or on the upper surface of the lower platforms on both sides of the convex epitaxial layer, the center position of the discrete side gate electrode must be directly opposite the center of the top gate electrode on the upper surface of the active region.
[0018] Furthermore, when multiple discrete side gate electrodes are disposed on the upper surface of the lower mesa of the stepped structure epitaxial layer, the multiple discrete side gate electrodes constitute a multi-side gate structure, and the center position of the multi-side gate structure must be directly opposite the center of the top gate electrode on the upper surface of the active region.
[0019] Furthermore, when multiple discrete side gate electrodes are disposed on the upper surface of the lower mesa on both sides of the epitaxial layer of the convex structure, the multiple discrete side gate electrodes disposed on the upper surface of the lower mesa on the same side constitute a multi-side gate structure, and the center position of the multi-side gate structure on both sides must be directly opposite to the center of the top gate electrode on the upper surface of the active region.
[0020] Furthermore, 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. By introducing a discrete side gate electrode structure, this invention enables the device to achieve a lower reverse conduction turn-on voltage compared to traditional HEMTs without reducing the forward threshold voltage, thus achieving lower reverse conduction losses.
[0023] 2. This device has a larger reverse saturation current than conventional devices, making it more advantageous for use as a reverse device.
[0024] 3. In terms of process implementation, the process steps are simpler compared to conventional gate-separated devices.
[0025] 4. Compared with the conduction method of parallel freewheeling diodes in the external circuit, this new structure solves this problem from the source and greatly saves costs.
[0026] 5. Since it does not use a Schottky diode, it is not limited by the turn-on voltage of parallel Schottky diode or PN junction diode technology. When operating in reverse, it can achieve a lower turn-on voltage and can even convert normally closed type to normally open type. Attached Figure Description
[0027] Figure 1 This is a diagram of the epitaxial layer structure in an embodiment of the present invention;
[0028] Figure 2 This is a structural diagram of a conventional HEMT device in an embodiment of the present invention;
[0029] Figure 3 This is a schematic diagram of the structure of a gallium nitride HEMT device with low reverse conduction threshold voltage according to an embodiment of the present invention;
[0030] Figure 4 for Figure 3 Cross-sectional view of a gallium nitride HEMT device with low reverse conduction threshold voltage;
[0031] Figure 5 This is a schematic diagram of the structure of a gallium nitride HEMT device with low reverse conduction threshold voltage according to an embodiment of the present invention;
[0032] Figure 6 This is a schematic diagram of the structure of a gallium nitride HEMT device with low reverse conduction threshold voltage according to an embodiment of the present invention;
[0033] Figure 7 This is a Cartesian coordinate transfer characteristic curve of a gallium nitride HEMT device with low reverse conduction threshold voltage and a conventional HEMT device in the forward conduction and reverse conduction states in an embodiment of the present invention.
[0034] Figure 8 This is a logarithmic coordinate graph showing the transfer characteristics of a gallium nitride HEMT device with a low reverse conduction threshold voltage and a conventional HEMT device in the forward and reverse conduction states, as described in this embodiment of the invention. Detailed Implementation
[0035] The technical solutions are illustrated in the following description with specific figures to provide a full understanding of this application. However, this application can be implemented in many other ways different from those described herein, and similar extended embodiments made by those skilled in the art without inventive effort are all within the scope of protection of this invention.
[0036] The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of this specification. The singular forms “a,” “described,” and “the” as used in one or more embodiments of this specification and in the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as 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 terms such as "first," "second," etc., may be used to describe various information in one or more embodiments of this specification, such information should not be limited to these terms. These terms are used only to distinguish similar objects and are not necessarily used to indicate the order or sequence of features described in one or more embodiments of this specification. Furthermore, the terms "possessing," "comprising," and similar expressions are intended to indicate coverage of 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 detailed list but may include inherent content related to those steps or modules that is not listed.
[0038] Example:
[0039] Conventional HEMT device structure as follows Figure 2 As shown, it includes an epitaxial layer 1, the upper part of which is an active region 2. An active electrode 3, a top gate electrode 4 and a drain electrode 5 are disposed on the upper surface of the active region 2. The source electrode 3 and the drain electrode 5 are located at the 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.
[0040] A low reverse threshold voltage gallium nitride HEMT device based on discrete gates, such as Figure 3 As shown, it includes an epitaxial layer 1 with a stepped structure;
[0041] Among them, the protruding part of the epitaxial layer 1, namely the upper platform, is called the active region 2. The active region 2 is provided with an active electrode 3, a top gate electrode 4 and a drain electrode 5. The source electrode 3 and the drain electrode 5 are located at the 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 disposed on the upper surface of the lower platform of the stepped epitaxial layer 1.
[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 sequentially from bottom to top.
[0044] In one embodiment, such as Figure 3 As shown, when using a stepped epitaxial layer 1, one side of the epitaxial layer 1 is etched to a depth exceeding the thickness of the barrier layer to form a stepped structure, with the protruding part being 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, both the source electrode 3 and the drain electrode 5 are multilayer metal stacks, which are Ti / Al / Ni / Au from bottom to top, with thicknesses of 20 / 100 / 10 / 100nm respectively.
[0047] In one embodiment, both the top gate electrode 4 and the discrete side gate electrode 6 are multilayer metal stacks, which are Ni / Au from bottom to top, with a thickness of 50 / 200nm.
[0048] In one embodiment, such as Figure 3 As shown, when a discrete side gate electrode 6 is disposed on the upper surface of the lower platform of the stepped epitaxial layer 1, the center position of the discrete side gate electrode 6 must be directly opposite the center of the top gate electrode 4 on the upper surface of the active region 2.
[0049] In one embodiment, such as Figure 6 As shown, when multiple discrete side gate electrodes 6 are disposed on the upper surface of the lower platform 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 directly opposite the center of the top gate electrode 4 on the upper surface of the active region 2.
[0050] In one embodiment, a discrete-gate, low reverse threshold voltage gallium nitride HEMT device, such as Figure 5 As shown, it includes an epitaxial layer 1 with a convex structure;
[0051] Among them, the protruding part of the epitaxial layer 1, namely the upper platform, is called the active region 2. The active region 2 is provided with an active electrode 3, a top gate electrode 4 and a drain electrode 5. The source electrode 3 and the drain electrode 5 are located at the 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 provided on the upper surface of the lower platform on both sides of the epitaxial layer 1 with a 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 sequentially from bottom to top.
[0054] In one embodiment, such as Figure 5 As shown, when using an epitaxial layer 1 with a convex structure, etching is performed on both sides of the epitaxial layer 1 to a depth exceeding the thickness of the barrier layer to form a convex structure, with the protruding part being the active region 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, both the source electrode 3 and the drain electrode 5 are multilayer metal stacks, which are Ti / Al / Ni / Au from bottom to top, with thicknesses of 20 / 100 / 10 / 100nm respectively.
[0057] In one embodiment, both the top gate electrode 4 and the discrete side gate electrode 6 are multilayer metal stacks, which are Ni / Au from bottom to top, with a thickness of 50 / 200nm.
[0058] In one embodiment, as shown in 5, when a discrete side gate electrode 6 is disposed on the upper surface of the lower platform 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 region 2.
[0059] In one embodiment, when multiple discrete side gate electrodes 6 are disposed on the upper surface of the lower platform on both sides of the epitaxial layer 1 of the convex structure, the multiple discrete side gate electrodes 6 disposed on the upper surface of the lower platform on the same side constitute a multi-side gate structure, and the center position of the multi-side gate structure on both sides must be directly opposite to the center of the top gate electrode 4 on the upper surface of the active region 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 discrete side gate electrode 6 has a rectangular cross-section.
[0062] In one embodiment, the discrete side gate electrode 6 has a triangular cross-section.
[0063] In one embodiment, the discrete side gate electrode 6 has a trapezoidal cross-section.
[0064] In one embodiment, such as Figure 7 and Figure 8 The diagram shows a comparison of the forward and reverse conduction characteristics of a gallium nitride HEMT device with a low reverse conduction threshold voltage and a conventional HEMT device. Figure 7 This is a graph of the transfer characteristics in rectangular coordinates. Figure 8 This is a graph of the transfer characteristics on logarithmic coordinates.
[0065] In the Silvaco simulation example Figure 7 and Figure 8The comparison of the transfer characteristic curves of the HEMT device of the present invention in both forward and reverse conduction states with those of a conventional HEMT device shows that the device of the present invention can significantly reduce the reverse conduction threshold voltage while maintaining a substantially constant forward conduction threshold voltage (achieving separation between the forward and reverse threshold voltages; the reverse threshold voltage decreases by approximately 0.25V at an electrode bias of 4V), whereas the forward and reverse threshold voltages of a conventional HEMT are identical, and their transfer characteristic curves almost overlap on logarithmic coordinates. Furthermore, the device of the present invention exhibits a large reverse conduction saturation current. These superior characteristics of the device of the present invention are of great significance for device implementation and reducing reverse conduction dead-zone losses.
[0066] This device can significantly reduce the reverse conduction threshold voltage while keeping the forward conduction threshold voltage basically unchanged. Furthermore, the reverse turn-on threshold voltage will decrease significantly as the reverse bias voltage of the device increases, and it can even achieve normal-on capability. This superior characteristic is of great significance for reducing reverse dead-time loss.
[0067] The above embodiments are merely preferred examples of the present invention and do not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, can make various modifications and changes in form and detail 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 protection scope of the claims of the present invention.
Claims
1. A gallium nitride HEMT device with low reverse threshold voltage based on discrete gate, characterized in that, An epitaxial layer (1) includes a convex or stepped structure; wherein, the protruding part of the epitaxial layer (1), i.e., the upper platform, is called the active region (2), and an active electrode (3), a top gate electrode (4), and a drain electrode (5) are disposed on the upper surface of the active region (2). The source electrode (3) and the drain electrode (5) are located at both 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); the top gate electrode (4), the source electrode (3), and the drain electrode (5) are located along the active region (2). The epitaxial layer (1) is arranged at intervals along the direction of extension; multiple discrete side gate electrodes (6) are provided on the upper surface of the lower mesa of the stepped structure epitaxial layer (1), and multiple discrete side gate electrodes (6) are provided on the upper surfaces of the lower mesa on both sides of the convex structure epitaxial layer (1); the epitaxial layer (1) includes a substrate, a nucleation layer, a buffer layer, an insertion layer and a barrier layer stacked sequentially from bottom to top; when multiple discrete side gate electrodes (6) are provided on the upper surface of the lower mesa of the stepped structure epitaxial layer (1), the multiple discrete side gate electrodes The electrode (6) forms a multi-side gate structure, and the center of the multi-side gate structure must be directly opposite the center of the top gate electrode (4) on the upper surface of the active region (2); multiple discrete side gate electrodes (6) are in contact with the sidewalls of the active region (2) and their top surfaces are flush with the upper surface of the active region (2); 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 part is the active region (2); when a convex structure is used When the epitaxial layer (1) is formed, etching is performed on both sides of the epitaxial layer (1) to a depth exceeding the thickness of the barrier layer to form a convex structure. The protruding part is the active region (2). When multiple discrete side gate electrodes (6) are set on the upper surface of the lower mesa on both sides of the epitaxial layer (1) of the convex structure, the multiple discrete side gate electrodes (6) set on the upper surface of the lower mesa on the same side constitute a multi-side gate structure. The center position of the multi-side gate structure on both sides must be directly opposite to the center of the top gate electrode (4) on the upper surface of the active region (2).
2. The gallium nitride HEMT device with low reverse threshold voltage based on discrete gate according to claim 1, 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 polarization effect.
3. A gallium nitride HEMT device based on discrete gates with low reverse threshold voltage according to claim 1, characterized in that, Both the source electrode (3) and the drain electrode (5) are multilayer metal stacks, which are Ti / Al / Ni / Au from bottom to top, with thicknesses of 20 / 100 / 10 / 100 nm respectively.
4. A gallium nitride HEMT device with low reverse threshold voltage based on discrete gates according to claim 1, characterized in that, The top gate electrode (4) and the discrete side gate electrode (6) are both made of multilayer metal stacks, which are Ni / Au from bottom to top, with a thickness of 50 / 200 nm.
5. A gallium nitride HEMT device based on discrete gates with low reverse threshold voltage 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.