An open-gate AlGaN / GaN heterojunction field-effect transistor with auxiliary gate structure and its application

Abstract

The present invention relates to an open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure and its application, belonging to the field of microelectronic research technology. Compared with conventional open-gate AlGaN / GaN heterojunction field-effect transistors, the present invention introduces a non-open auxiliary gate structure, effectively improving the saturation characteristics of open-gate devices. The auxiliary gate is located between the drain of the device and the open main gate. Its purpose is to fix the surface potential of the region in which it is located, so that the current saturation of the open-gate device is freed from dependence on the surface virtual gate, thereby improving the saturation characteristics of the device and making it more stable and controllable. By applying different potentials to the main gate and the auxiliary gate, different device operating modes can be obtained, which makes the application of the present invention in circuits more flexible and more suitable for the increasingly complex field of integrated circuits.

Description

Technical Field

[0001] The present invention relates to an open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure and applications thereof, belonging to the technical field of microelectronics research. Background Art

[0002] AlGaN / GaN heterojunction field-effect transistors (HFETs) are an important representative of wide-bandgap semiconductor electronic devices. They have advantages such as high breakdown voltage and high electron mobility and are widely used in high-frequency and high-power fields. There are also many patent documents reporting on AlGaN / GaN HFETs, such as: CN107017293A, CN106876458A, CN106783961A, CN104009076A, CN106876457A, etc.

[0003] In addition, CN106783963A discloses an AlGaN / GaN heterojunction field effect transistor with a partial intrinsic GaN cap layer. This new transistor structure introduces an intrinsic GaN cap layer at the edge of the transistor gate. The intrinsic GaN cap layer reduces the two-dimensional electron gas concentration of the conductive channel in this area, achieving an electric field modulation effect. By generating a new electric field peak, the high electric field at the gate edge is reduced, making the electric field distribution on the transistor surface more uniform. CN106783960A discloses a stepped p-GaN enhanced AlGaN / GaN heterojunction field effect transistor. This transistor structure introduces a p-type GaN cap layer at the edge of the transistor gate, and the thickness of the cap layer is less than the thickness of the p-type GaN dielectric layer under the gate. The p-type GaN cap layer reduces the two-dimensional electron gas concentration of the conductive channel in this area, achieving an electric field modulation effect. By generating a new electric field peak, the high electric field at the gate edge is reduced, making the electric field distribution on the transistor surface more uniform, thereby improving the breakdown characteristics of the device.

[0004] The inventor of the present invention's previous patent document CN202110080815.5 discloses a new type of AlGaN / GaN heterojunction field-effect transistor and its application, in which the gate is set to an open gate structure. As a new type of AlGaN / GaNHFETs, open-gate devices can simply achieve a wide range of control of the threshold voltage by changing the opening width, and have broad application prospects in the field of low-power Class A voltage amplifiers. However, the saturation mechanism of conventional open-gate devices is related to the virtual gate formed by surface electron injection. Surface electron injection depends on the trap state on the surface of the device, and the number of surface trap states is difficult to control artificially. This means that the saturation process of conventional open-gate devices is highly random, and the saturation characteristics are usually poor. To obtain open-gate devices with good saturation characteristics, it can only be achieved through large-scale preparation and screening.

[0005] Therefore, it is urgent and important to study a new open-gate AlGaN / GaN HFET that can effectively improve the saturation characteristics of the device. Currently, there are no reports on the use of open gate and auxiliary gate to jointly control the saturation characteristics. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides an open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure and its application.

[0007] Explanation of terms

[0008] The channel refers to a thin semiconductor layer between the source and drain regions in a field-effect transistor, where the flow of current is controlled by the gate potential.

[0009] The technical solutions of the present invention are as follows:

[0010] An open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure has an overall device structure similar to that of a conventional open-gate AlGaN / GaN heterojunction field-effect transistor, including a source, a drain, and a gate located between the source and the drain. The gate is a dual-gate structure comprising a main gate and an auxiliary gate, and the main gate includes a lateral opening.

[0011] According to the present invention, preferably, the auxiliary grid has no transverse openings.

[0012] According to the present invention, preferably, the auxiliary gate is located between the drain and the main gate.

[0013] According to the present invention, preferably, 0<auxiliary gate length<distance between the main gate and the drain.

[0014] Most preferably, the distance between the main gate and the drain is 16 μm, and the length of the auxiliary gate is 4-10 μm.

[0015] According to the present invention, preferably, auxiliary gate width=main gate width+opening width=total channel width.

[0016] According to the present invention, preferably, 0<the distance between the auxiliary gate and the drain electrode<the distance between the main gate and the drain electrode-the length of the auxiliary gate.

[0017] According to the present invention, preferably, 0<main gate width<total channel width.

[0018] According to the present invention, preferably, 0<main gate lateral opening width<total channel width.

[0019] According to the present invention, preferably, 0<distance between the main gate and the source ≤ distance between the main gate and the drain.

[0020] According to the present invention, the operating region of a conventional open-gate AlGaN / GaN heterojunction field-effect transistor is divided into a gate region and an open region. As the gate bias increases in a negative direction (from zero to a negative value), the channel two-dimensional electron gas density in the gate region decreases until it is depleted. However, since the open region is not covered by gate strips, its two-dimensional electron gas density does not change with gate bias and remains conductive. At this point, the device current saturation mechanism is completely determined by the current saturation mechanism in the open region.

[0021] Ideally, the surface of the gateless opening region is at a floating potential. As the drain-source voltage increases, the surface potential increases along with the channel potential. Therefore, the current cannot saturate with increasing drain-source voltage until the channel electrons reach their saturation drift velocity. In actual devices, due to the presence of surface trap states, when a positive drain-source voltage is applied to the device, electrons are injected through the source into the device surface and captured by the surface trap states, causing the device's surface potential to drop. This creates a negative potential difference between the surface and the channel, equivalent to a negatively biased virtual gate on the device surface. As the drain-source voltage increases, the potential near the drain end of the channel rises, and the absolute value of the potential difference with the virtual gate on the surface increases. When this increases to a certain level, the channel pinches off at this location, achieving channel current saturation.

[0022] The formation of virtual gates depends largely on surface trap states, which are primarily related to the material growth process. Their density, location, and energy state are difficult to precisely control. If there are too few surface trap states, current saturation in the device will be difficult to achieve; if there are too many surface trap states, the device's output and leakage characteristics will be affected. Furthermore, due to the random nature of surface trap states, devices with good saturation characteristics can only be obtained through large-scale screening and preparation, making them difficult to achieve through human control.

[0023] The present invention has an open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure. By introducing the auxiliary gate structure, the saturation characteristics of the open-gate device are effectively improved. The auxiliary gate is located between the main gate and the drain, and the gate strips are not open. When the device is operating, a constant bias voltage (generally 0V or a negative bias voltage) is applied to the auxiliary gate to fix the surface potential of the auxiliary gate region of the device so that it no longer changes with changes in the channel potential. In this case, when a large positive drain-source voltage is applied to the device, the channel potential below the auxiliary gate region of the device will increase accordingly. On the other hand, due to the presence of the auxiliary gate, the surface potential of this region is fixed, so a negative potential difference is formed between the auxiliary gate and the channel below, thereby consuming the channel two-dimensional electron gas in this region. As the drain-source voltage increases, the channel potential below the auxiliary gate increases, and a larger absolute value negative potential difference will be generated between the auxiliary gate and the channel below, consuming more two-dimensional electron gas, and eventually the channel is pinched off, so that the current reaches saturation.

[0024] With the introduction of the auxiliary gate structure, the device's surface potential is controlled by the auxiliary gate, rather than the virtual gate formed by surface electron injection. This frees the device's saturation process from reliance on surface trap states. The position and potential of the auxiliary gate are manually determined and can be freely adjusted according to specific needs. This makes it more stable and controllable than the virtual gate formed by surface electron injection, thereby improving the device's saturation characteristics and significantly enhancing both controllability and stability.

[0025] On the other hand, by applying different potentials to the main gate and the auxiliary gate, the open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure of the present invention can achieve multiple operating modes.

[0026] Mode 1: The main gate is left open, with only the auxiliary gate applying a varying gate bias. In this mode, the device channel current is controlled by the unconnected auxiliary gate, equivalent to a traditional AlGaN / GaN heterojunction field-effect transistor. In this mode, the gate bias has a stronger ability to control the channel current, but the voltage range for controlling the channel current is narrower, and the threshold voltage is higher.

[0027] Mode 2: A variable gate bias is applied to the main gate, while the auxiliary gate potential is held constant at 0V. In this mode, the device channel current is controlled by the open main gate, while the auxiliary gate acts to stabilize the surface potential. In this mode, the gate bias has a weaker ability to control the channel current, resulting in a wider voltage range and a lower threshold voltage, similar to conventional open-gate devices. However, the presence of the auxiliary gate significantly improves the device's saturation characteristics.

[0028] Mode 3: A varying gate bias is applied to the main gate, while the auxiliary gate potential remains constant at a negative value. In this case, the device's control and characteristics are similar to those in Mode 2. However, the lower auxiliary gate potential depletes the channel's two-dimensional electron gas (2DEG) in the corresponding region, resulting in an overall decrease in the device's channel current at the same gate bias. In practical circuit applications, lower current means lower DC power loss, making Mode 3 more suitable for low-power applications than Mode 2.

[0029] According to the present invention, the open-gate AlGaN / GaN heterojunction field-effect transistor with the auxiliary gate structure is used in the preparation of electronic integrated circuits.

[0030] Anything not described in detail in the present invention is based on the existing technology in this field.

[0031] The beneficial effects of the present invention are:

[0032] 1. The present invention introduces an unopened auxiliary gate in the main gate-drain region that is originally not covered by an electrode. After the auxiliary gate structure is introduced, the surface potential of the device can be fixed by applying a zero bias voltage to the auxiliary gate, and the potential difference between the auxiliary gate and the channel can be used to achieve channel current saturation, thereby significantly improving the saturation characteristics of the device.

[0033] 2. The present invention comprises a four-terminal device consisting of a source, a drain, an open main gate and an auxiliary gate. By applying different bias voltages to the open main gate and the auxiliary gate, a variety of device operating modes can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1-Figure 3 The following are schematic diagrams of three different AlGaN / GaN heterojunction field effect transistor structures. Figure 1 This is the conventional device used for comparison in Comparative Example 1; Figure 2 This is a conventional open-gate device used for comparison in Comparative Example 2; Figure 3 This is the open gate device with the auxiliary gate structure in Example 1 of the present invention, wherein S represents the source of the device, G represents the gate of the device, D represents the drain of the device, G1 and G2 represent the main gate and the auxiliary gate, respectively.

[0035] Figure 4a-4e : The current-voltage characteristic curves of the AlGaN / GaN heterojunction field effect transistors in Example 1 of the present invention and Comparative Examples 1-2. The horizontal axis is voltage and the vertical axis is current. Figure 4a is the current-voltage characteristic curve of the conventional device used for comparison in Comparative Example 1; Figure 4b is the current-voltage characteristic curve of the conventional open-gate device used for comparison in Comparative Example 2; Figure 4c 1 is a current-voltage characteristic curve of an open-gate device with an auxiliary gate structure according to embodiment 1 of the present invention, when the device operates in mode 1; Figure 4d 1 is a current-voltage characteristic curve of an open-gate device with an auxiliary gate structure according to embodiment 1 of the present invention, when the device operates in mode 2; Figure 4e This is a current-voltage characteristic curve of an open-gate device with an auxiliary gate structure according to Example 1 of the present invention. At this time, the device operates in mode 3 and the auxiliary gate bias is -1V. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to embodiments and accompanying drawings, but is not limited thereto.

[0037] Example 1:

[0038] An open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure comprises a source S, a drain D, and a gate G located between the source S and the drain D. The gate G is a dual-gate structure comprising a main gate G1 and an auxiliary gate G2. The main gate G1 includes a lateral opening to form two different working areas, namely a main gate area and an opening area.

[0039] Its device structure is as follows Figure 3 As shown, the main gate length of the device (L G1 ) is 40μm, the distance between the main gate and the source (L G1s ) is 6μm, the distance between the main gate and the drain (L c1D ) is 16 μm, the total channel width (W) is 100 μm, and the width of the opening area (W O ) is 3μm, and the auxiliary gate length is (L G2 ) 10μm, the distance between the auxiliary gate and the drain (L G2D ) is 3μm.

[0040] Example 2:

[0041] The open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure as described in Example 1 is different in that:

[0042] The main gate length of the device (L G1 ) is 4μm, the distance between the main gate and the source (L G1S ) is 6μm, the distance between the main gate and the drain (L G1D ) is 16 μm, the total channel width (W) is 100 μm, and the width of the opening area (W O ) is 3μm, and the auxiliary gate length is (L G2 )4μm, the distance between the auxiliary gate and the drain (L G2D ) is 6μm.

[0043] Example 3:

[0044] The open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure as described in Example 1 is different in that:

[0045] The main gate length of the device (L G1 ) is 80μm, the distance between the main gate and the source (L G1S ) is 10 μm, the distance between the main gate and the drain (L G1D ) is 10 μm, the total channel width (W) is 100 μm, and the width of the opening area (W O ) is 5μm, and the auxiliary gate length is (L G2 )4μm, the distance between the auxiliary gate and the drain (L G2D ) is 3μm.

[0046] Example 4:

[0047] The open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure as described in Example 1 is different in that:

[0048] The main gate length of the device (L G1 ) is 20μm, the distance between the main gate and the source (L G1S ) is 6μm, the distance between the main gate and the drain (L G1D ) is 16μm, the total channel width (W) is 80μm, and the width of the opening area (W O ) is 4μm, and the auxiliary gate length is (L G2 )6μm, the distance between the auxiliary gate and the drain (L G2D ) is 5μm.

[0049] Comparative Example 1

[0050] The gate of the conventional AlGaN / GaN heterojunction field effect transistor is not opened and has no auxiliary gate structure. The dimensions of other parts are the same as those of the device in Example 1. The device structure is as follows: Figure 1 shown.

[0051] Comparative Example 2

[0052] Conventional open-gate AlGaN / GaN heterojunction field effect transistor, without auxiliary gate structure, and other dimensions are the same as those of the device in Example 1. The device structure is as follows: Figure 2 shown.

[0053] Test example

[0054] By applying different potentials to the main gate and the auxiliary gate, the open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure of the present invention can achieve multiple operating modes.

[0055] Mode 1: The main gate is left open, with only the auxiliary gate applying a varying gate bias. In this mode, the device channel current is controlled by the unconnected auxiliary gate, equivalent to a traditional AlGaN / GaN heterojunction field-effect transistor. In this mode, the gate bias has a stronger ability to control the channel current, but the voltage range for controlling the channel current is narrower, and the threshold voltage is higher.

[0056] Mode 2: A variable gate bias is applied to the main gate, while the auxiliary gate potential is held constant at 0V. In this mode, the device channel current is controlled by the open main gate, while the auxiliary gate acts to stabilize the surface potential. In this mode, the gate bias has a weaker ability to control the channel current, resulting in a wider voltage range and a lower threshold voltage, similar to conventional open-gate devices. However, the presence of the auxiliary gate significantly improves the device's saturation characteristics.

[0057] Mode 3: A varying gate bias is applied to the main gate, while the auxiliary gate potential remains constant at a negative value. In this case, the device's control and characteristics are similar to those in Mode 2. However, the lower auxiliary gate potential depletes the channel's two-dimensional electron gas (2DEG) in the corresponding region, resulting in an overall decrease in the device's channel current at the same gate bias. In practical circuit applications, lower current means lower DC power loss, making Mode 3 more suitable for low-power applications than Mode 2.

[0058] Figure 4a-4e is the current-voltage characteristic curve of the device, Figure 4a Corresponding to proportion 1, Figure 4b For ratio 2, Figure 4c-4e Corresponding to embodiment 1, the difference lies in the different working modes of the device. Figure 4c Corresponding mode 1, Figure 4d Corresponding to mode 2, Figure 4d This corresponds to mode 3 (the specific value of the constant negative potential of the auxiliary gate is -1V).

[0059] from Figure 4c It can be seen from the figure that when the device of Example 1 works in Mode 1, its gate bias has a strong ability to regulate the drain-source current, but the effective regulation range is very small, and the threshold voltage is about -2.5V. At this time, the current-voltage curve of the device is Figure 4a The curves shown are very similar, which indicates that when operating in Mode 1, the device of Example 1 is equivalent to a conventional AlGaN / GaN heterojunction field-effect transistor.

[0060] from Figure 4d It can be seen from the figure that when the device of Example 1 works in Mode 2, its gate bias voltage has a very weak ability to regulate the drain-source current, but the effective regulation range is very large, and the threshold voltage is about -36V. Figure 4b The current-voltage characteristics shown are similar. However, in Figure 4b In the figure, the saturation voltage of the device under different gate bias voltages is very large, especially when the absolute value of the negative gate bias voltage is small, the channel current increases along the arc as the drain-source voltage increases, and there is no obvious saturation sign until the drain-source voltage reaches 20V. In contrast, Figure 4d In the experiment, the saturation voltage of the device at different gate biases is around 2V, and there is a clear distinction between the linear region and the saturation region. This shows that the saturation characteristics of the open-gate device have been significantly improved by introducing the auxiliary gate structure.

[0061] from Figure 4e It can be seen from the figure that when the device of Example 1 works in Mode 3, its current-voltage characteristics still show the characteristics of weak gate bias control ability, large effective control range, low threshold voltage, and good saturation characteristics, which is different from the characteristics of the device of Example 1 when it works in Mode 2 ( Figure 4d). The difference from Mode 2 is that when the device operates in Mode 3, the channel current under the same main gate bias is reduced overall, making it more suitable for low-power applications.

Claims

1. An open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure, characterized in that: The transistor includes a source, a drain, and a gate located between the source and the drain, wherein the gate is a double-gate structure, the gate includes a main gate and an auxiliary gate, and the main gate includes a lateral opening; The auxiliary gate has no lateral opening and is located between the drain and the main gate. The auxiliary gate width is equal to the main gate width. Depth + opening width = total channel width.

2. The open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure according to claim 1, characterized in that: 0<auxiliary gate length<distance between main gate and drain.

3. The open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure according to claim 1, wherein: The distance between the main gate and the drain is 16 μm, and the length of the auxiliary gate is 4-10 μm.

4. The open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure according to claim 1, wherein: 0<the distance between the auxiliary gate and the drain<the distance between the main gate and the drain-the length of the auxiliary gate.

5. The open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure according to claim 1, wherein: 0<main gate width<total channel width.

6. The open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure according to claim 1, wherein: 0<main gate lateral opening width<total channel width.

7. The open-gate AlGaN / GaN heterojunction field-effect transistor with an auxiliary gate structure according to claim 1, wherein: 0<the distance between the main gate and the source ≤ the distance between the main gate and the drain.

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