Hybrid enhanced / depleted gate structure for high electron mobility transistor

Abstract

An HEMT includes a hybrid gate contact that includes an enhanced gate portion and a depleted gate portion. The depletion gate portion acts as a buffer that reduces the large electric field peak that would otherwise already exist at the enhancement gate portion if there is no depletion gate portion. On the contrary, the large electric field peak value is divided into two smaller electric field peak values; a first smaller electric field peak is at a drain contact side of the depletion gate portion and a second smaller electric field peak is at a drain contact side of the enhancement gate portion. The use of such hybrid gate contacts allows for greater ability to adjust and reduce the electric field peaks, as compared to HEMT with only enhanced gates, thus allowing for reduction of the overall size of the HEMT, and / or allowing the HEMT to handle higher voltages and currents.

Description

Background Art

[0001] Electronic circuits often include transistors that act as electronic switches to regulate or control current in parts of the circuit. One type of transistor is a field effect transistor in which a voltage is applied to a gate terminal to turn the transistor on and off. A semiconductor channel region is disposed between a drain terminal and a source terminal. When the transistor is turned on, current flows through the semiconductor channel region between the source terminal and the drain terminal. When the transistor is turned off, less or no current flows through the semiconductor channel region between the source terminal and the drain terminal. A gate terminal is disposed over the semiconductor channel region between the source terminal and the drain terminal. The voltage on the gate terminal creates a field that affects whether the semiconductor channel region conducts current - hence the term "field effect transistor".

[0002] Silicon has traditionally been used to make transistors. However, wider bandgap semiconductor materials can be used to make transistors that conduct higher power and operate at higher efficiencies than silicon transistors. Silicon carbide (SiC), aluminum nitride (AlN), zinc oxide (ZnO), and gallium nitride (GaN) are each examples of wide bandgap semiconductor materials that can be used in power electronic devices. GaN is an example of a semiconductor material formed by two layers of different semiconductor materials forming a heterojunction therebetween.

[0003] The two semiconductor materials may have sufficiently different band gaps so that when brought together, the combined band gap just drops below the Fermi level in the channel layer. This means that electrons can flow freely in this region. This region is thin in depth and forms a plane parallel to the upper surface of the channel region. Therefore, this region is called a two-dimensional electron gas "2DEG", where the term "two-dimensional" emphasizes its planar form, and the term "electron gas" emphasizes 2DEG due to the high mobility of electrons in this region. Therefore, the 2DEG region is highly conductive and is also commonly referred to as an "electron sea". The 2DEG region can form a channel region of a power semiconductor to allow a high current with relatively low resistance to pass. Field effect transistors using such 2DEG are called "high electron mobility transistors" (or HEMTs).

[0004] The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above.Rather, this background is provided merely to illustrate one exemplary technology area in which some embodiments described herein may be practiced. Summary of the invention

[0005] This summary is provided to introduce a series of concepts in a simplified form, which are further described in the detailed description below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to help determine the scope of the claimed subject matter.

[0006] Embodiments described herein relate to a circuit for controlling a high electron mobility transistor (HEMT). The HEMT includes a hybrid gate contact that includes an enhancement gate portion and a depletion gate portion. The circuit further includes a controller that can be used to apply various voltages to the enhancement gate portion and the depletion gate portion. For reasons to be described, the use of such a hybrid gate contact allows for greater ability to adjust and reduce electric field peaks, thereby allowing the overall size of the HEMT to be reduced, and / or allowing the HEMT to handle higher voltages and currents, as compared to a HEMT with only an enhancement gate.

[0007] The HEMT is formed by growing an epitaxial layer on a substrate along an epitaxial growth direction. The epitaxial layer includes a channel semiconductor layer and a barrier semiconductor layer epitaxially grown on the channel layer. The interface of the barrier layer and the channel layer defines a heterojunction that induces a two-dimensional electron gas (2DEG) in the channel semiconductor layer. The 2DEG extends perpendicular to the epitaxial growth direction. The HEMT also includes a source contact and a drain contact that are each in conductive contact with the 2DEG of the channel layer. Therefore, the 2DEG defines a channel of the transistor, and current can flow from the drain contact to the source contact through the channel. The HEMT also includes a gate contact disposed above the barrier layer along the epitaxial growth direction, and the gate contact is further disposed between the source contact and the drain contact perpendicular to the epitaxial growth direction. The voltage applied to the gate contact controls whether the 2DEG is continuous or discontinuous between the source contact and the drain contact, and thus controls whether the HEMT is turned on or off.

[0008] Because HEMTs are used to control high voltages and currents, the high voltage difference between the gate contact and the drain contact can cause large electric field peaks to be generated in the channel layer on the side of the gate contact closer to the drain contact, particularly when the HEMT is turned off. To help reduce the magnitude of the electric field peak on the drain contact side of the gate contact, a HEMT according to the principles described herein has a hybrid gate contact including an enhancement gate portion and a depletion gate portion in series, wherein the depletion gate portion is closer to the drain contact.

[0009] A p-doped semiconductor portion is formed between the enhancement gate portion and the barrier layer along the epitaxial growth direction, so that when zero volts are applied to the enhancement gate portion, the 2DEG is discontinuous under the enhancement gate portion. On the other hand, when zero volts are applied to the depletion gate portion, the depletion gate portion causes the 2DEG to be continuous under the depletion gate portion. For example, this may be the case if there is no p-doped semiconductor portion between the depletion gate portion and the barrier layer.

[0010] In addition to the buffering performed by the selected field plate, the depletion gate portion acts as an additional buffer that reduces the large electric field peak that would otherwise exist at the enhancement gate portion if the depletion gate portion was not present. Thus, instead of having a single large electric field peak at the drain side of the enhancement gate portion, the electric field peak is split into two smaller electric field peaks; the first smaller electric field peak at the drain contact side of the depletion gate portion, and the second smaller electric field peak at the drain contact side of the enhancement gate portion. Furthermore, the hybrid gate helps reduce the overall magnitude of the electric field in the channel layer near the drain contact, which allows the HEMT to be designed so that the drain contact can be closer to the gate contact, thus allowing the overall size of the HEMT to be reduced. Additionally, the reduction in the electric field peak across the channel layer allows the HEMT to be used to control higher voltages and currents than would have been possible without the hybrid gate contact.

[0011] Additional features and advantages will be set forth in the following description and, in part, will be apparent from the description or may be learned through practice of the teachings herein. The features and advantages of the present invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. The features of the present invention will become more fully apparent from the following description and the appended claims or may be learned through practice of the present invention as set forth below. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to describe the manner in which the above-recited and other advantages and features can be obtained, a more particular description of the subject matter briefly described above will emerge by reference to specific embodiments that are illustrated in the accompanying drawings. Understanding that these drawings depict only typical embodiments and are, therefore, not to be considered limiting in scope, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:

[0013] Figure 1 The diagram illustrates a circuit in which the principles described herein may be practiced and is merely one example of a circuit consistent with the principles described herein;

[0014] Figure 2A illustrates a cross-sectional view of an enhancement mode high electron mobility transistor (HEMT);

[0015] Figure 2B The diagram corresponds to Figure 2A Electric field contour diagram of HEMT;

[0016] Figure 3A illustrates a cross-sectional view of a HEMT with a hybrid gate contact 360, according to principles described herein, Figure 3A The HEMT is available in Figure 1 An example of a HEMT included in a circuit of;

[0017] Figure 3B The diagram corresponds to Figure 3A Electric field contour diagram of HEMT;

[0018] Figure 4 The diagram shows a superimposed Figure 2B and Figure 3B The electric field diagram of the electric field contour shown in;

[0019] Figure 5A Pictured Figure 2A Example of an enhanced gate contact for a HEMT;

[0020] Figure 5B Pictured Figure 3A Example of a hybrid gate contact for a HEMT.

[0021] Figure 5C illustrates an exemplary embodiment of a hybrid gate contact that may be incorporated into a HEMT; and

[0022] Figure 5D Another exemplary embodiment of a hybrid gate contact that may be incorporated into a HEMT is illustrated. DETAILED DESCRIPTION

[0023] Embodiments described herein relate to a circuit for controlling a high electron mobility transistor (HEMT). The HEMT includes a hybrid gate contact that includes an enhancement gate portion and a depletion gate portion. The circuit further includes a controller that can be used to apply various voltages to the enhancement gate portion and the depletion gate portion. For reasons to be described, the use of such a hybrid gate contact allows for greater ability to adjust and reduce electric field peaks, thereby allowing the overall size of the HEMT to be reduced, and / or allowing the HEMT to handle higher voltages and currents, as compared to a HEMT with only an enhancement gate.

[0024] The HEMT is formed by growing an epitaxial layer on a substrate along an epitaxial growth direction. The epitaxial layer includes a channel semiconductor layer and a barrier semiconductor layer epitaxially grown on the channel layer. The interface of the barrier layer and the channel layer defines a heterojunction that induces a two-dimensional electron gas (2DEG) in the channel semiconductor layer. The 2DEG extends perpendicular to the epitaxial growth direction. The HEMT also includes a source contact and a drain contact that are each in conductive contact with the 2DEG of the channel layer. Therefore, the 2DEG defines a channel of the transistor, and current can flow from the drain contact to the source contact through the channel. The HEMT also includes a gate contact disposed above the barrier layer along the epitaxial growth direction, and the gate contact is further disposed between the source contact and the drain contact perpendicular to the epitaxial growth direction. The voltage applied to the gate contact controls whether the 2DEG is continuous or discontinuous between the source contact and the drain contact, and thus controls whether the HEMT is turned on or off.

[0025] Because HEMTs are used to control high voltages and currents, the high voltage difference between the gate contact and the drain contact can cause large electric field peaks to be generated in the channel layer on the side of the gate contact closer to the drain contact, particularly when the HEMT is turned off. To help reduce the magnitude of the electric field peak on the drain contact side of the gate contact, a HEMT according to the principles described herein has a hybrid gate contact including an enhancement gate portion and a depletion gate portion in series, wherein the depletion gate portion is closer to the drain contact.

[0026] A p-doped semiconductor portion is formed between the enhancement gate portion and the barrier layer along the epitaxial growth direction, so that when zero volts are applied to the enhancement gate portion, the 2DEG is discontinuous under the enhancement gate portion. On the other hand, when zero volts are applied to the depletion gate portion, the depletion gate portion causes the 2DEG to be continuous under the depletion gate portion. For example, this may be the case if there is no p-doped semiconductor portion between the depletion gate portion and the barrier layer.

[0027] In addition to the buffering performed by the selected field plate, the depletion gate portion acts as an additional buffer that reduces the large electric field peak that would otherwise exist at the enhancement gate portion if the depletion gate portion was not present. Thus, instead of having a single large electric field peak at the drain side of the enhancement gate portion, the electric field peak is split into two smaller electric field peaks; the first smaller electric field peak at the drain contact side of the depletion gate portion, and the second smaller electric field peak at the drain contact side of the enhancement gate portion. Furthermore, the hybrid gate helps reduce the overall magnitude of the electric field in the channel layer near the drain contact, which allows the HEMT to be designed so that the drain contact can be closer to the gate contact, thus allowing the overall size of the HEMT to be reduced. Additionally, the reduction in the electric field peak across the channel layer allows the HEMT to be used to control higher voltages and currents than would have been possible without the hybrid gate contact.

[0028] Figure 1 The circuit 100 is illustrated in which the principles described herein may be practiced and is merely one example of a circuit consistent with the principles described herein. The circuit 100 includes a HEMT 101 and a controller 102 electrically connected via a connection 103. Figure 1 HEMT 101 is abstractly illustrated in FIG. Figure 3A A more specific example of the HEMT 101 is described. However, in broad terms, the HEMT 101 is a field effect transistor and thus has a drain contact ( Figure 1 not shown) and the source contact ( Figure 1 1 and 2. A gate contact (eg, hybrid gate contact 110) that flows between the transistors (not shown).

[0029] More specifically, the gate contact of the HEMT 101 is a hybrid gate contact 110 that includes an enhancement gate portion 111 and a depletion gate portion 112. The controller 102 applies various voltages to the hybrid gate contact 110 (via the connection 103). For example, the controller 102 may apply an on voltage (e.g., positive 6 volts) to the hybrid gate contact 110 to turn the HEMT 101 on, and the controller 102 may apply an off voltage (e.g., zero volts) to the hybrid gate contact 110 to turn the HEMT 101 off. At a high level, the use of the hybrid gate contact 110 allows the HEMT 101 to operate at higher voltage and current limits, as compared to a HEMT having only an enhancement gate contact, and allows the overall size of the HEMT 101 to be reduced. This will be discussed later. Figure 3A and Figure 3B The reasons why these benefits may be achieved, as well as additional exemplary structures and exemplary operations of the HEMT 101 are explained in more detail.

[0030] To fully understand Figure 1 The discussion will now return to the discussion of why the hybrid gate contact 110 is advantageous. Figure 2A and Figure 2B Discussion of how a HEMT with only an enhancement gate contact can be operated. Figure 2A A cross-sectional view of a HEMT 200 is illustrated. Figure 2A Further illustrated is a coordinate system 201. For ease and clarity of explanation only, the direction indicated by the arrow on the y-axis in the coordinate system 201 will be referred to as the direction of epitaxial growth, and the x-axis will be referred to as the direction perpendicular to the epitaxial growth. Thus, the direction in the positive y-direction will sometimes be referred to as being in the "epitaxial growth direction", and the direction parallel to the x-axis will sometimes be referred to as being "perpendicular to the epitaxial growth direction".

[0031] HEMT 200 includes epitaxial layers including a channel layer 210 and a barrier layer 220 epitaxially grown on the channel layer 210 along an epitaxial growth direction. The interface between the channel layer 210 and the barrier layer 220 defines a heterojunction that induces a two-dimensional electron gas (referred to herein as "2DEG") 230 within the channel layer 210, through which current can flow when the HEMT 200 is turned on. This is because the channel layer 210 and the barrier layer 220 are made of different semiconductor materials that have sufficiently different band gaps so that when connected together, the combined band gap drops just below the Fermi level within the channel layer 210, thereby forming a region of high electron concentration (2DEG 230). By way of example only, if channel layer 210 is composed of gallium nitride (GaN) and barrier layer 220 is composed of aluminum gallium nitride (AlGaN), the band gap difference will be sufficient to produce 2DEG 230. However, the principles described herein are not limited to the types of semiconductor materials that constitute channel layer 210 and barrier layer 220.

[0032] HEMT 200 further includes a source contact 240, a drain contact 250, and a gate contact 260. Source contact 240 and drain contact 250 are disposed at opposite ends (perpendicular to the epitaxial growth direction) of 2DEG 230. More specifically, Figure 2A , the source contact 240 is disposed over the left side of the top surface of the 2DEG 230 , and the drain contact 250 is disposed over the right side of the top surface of the 2DEG 230 .

[0033] The gate contact 260 is disposed on the barrier layer 220 along the epitaxial growth direction and is disposed perpendicular to the epitaxial growth direction between the source contact 240 and the drain contact 250. The portion of the 2DEG 230 below the gate contact 260 is affected by a voltage applied to the gate contact 260. For example, when the HEMT 200 is turned on, the 2DEG region 230 is continuous below the gate contact 260, thereby allowing current to flow freely between the drain contact 250 and the source contact 240. However, when the HEMT 200 is turned off, the 2DEG region 230 is discontinuous below the gate contact 260, thereby preventing current from flowing between the drain contact 250 and the source contact 240.

[0034] The HEMT 200, which acts as an enhancement-mode HEMT, includes a p-doped semiconductor portion 261 between the gate contact 260 and the barrier layer 220 along the epitaxial growth direction. When zero volts is applied to the gate contact 260, the p-doped semiconductor portion 261 causes the 2DEG 230 to be discontinuous under the gate contact 260. Therefore, in order to cause the 2DEG 230 under the gate contact 260 to become continuous and thus turn on the HEMT 200, a sufficiently positive voltage is applied to the gate contact 260. As an example, the sufficiently positive voltage may be a voltage greater than the gate-to-source threshold voltage of the HEMT 200.

[0035] As previously expressed, HEMTs are used to control high voltages and currents. Thus, while HEMT 200 is off, source contact 240 and gate contact 260 may have zero volts applied to them, and a large positive voltage (e.g., hundreds of volts) may be present at drain contact 250. The large voltage difference between drain contact 250 and gate contact 260 may induce a large electric field peak within channel layer 210 (particularly, at the drain side of gate contact 260), as illustrated at location X1. To illustrate this, Figure 2B The diagram corresponds to Figure 2A The electric field profile of HEMT 200. Figure 2A and Figure 2B Align in Figure 2A The electric field at each horizontal position in Figure 2B The electric field is shown in the figure below. To explain why a large electric field is generated, a brief explanation of the electric field will now be described.

[0036] The magnitude of the electric field between two points of different voltages is proportional to the magnitude of that voltage difference and inversely proportional to the distance between the two points. When a positive voltage is applied on the drain, the voltage drops from the drain edge to the p-gate edge. The electric field is proportional to the applied voltage, and as the voltage increases, the electric field also increases. HEMTs are meant to withstand high voltages from drain to gate, which means withstanding large electric fields. At the edge of the gate, the electric field lines tend to crowd and cause electric field peaks due to the abrupt nature of the p-gate termination.

[0037] If the electric field peaks are too large, problems may occur in the HEMT. Figure 2A In the HEMT 200 of FIG. 2 , if the electric field peak 291 at position X1 is too large, it will cause the HEMT 200 to degrade relatively quickly. This is partly because the large electric field peak at the drain side of the gate contact 260 causes "gate current leakage", where some electrons pass through the barrier layer 220 under the gate contact 260 and induce a small current between the gate contact 260 and the drain contact 250. This causes HEMT degradation and faster aging of the HEMT. To prevent large electric field peaks, a field plate can be used.

[0038] For example, Figure 2A The HEMT 200 includes field plates 270 and 280. The field plates 270 and 280 are each disposed above the barrier layer 220 in the epitaxial growth direction, but each is further from the 2DEG 230 than the gate contact 260 in the epitaxial growth direction. As a side note, the regions below the field plates 270 and 280 in the epitaxial growth direction and the regions between the rest of the elements of the HEMT 200 may be composed of a dielectric material that contributes to structural stability and electrical isolation between the elements of the HEMT 200. Each of the field plates 270 and 280 may be grounded, or may have a voltage applied thereto. In any case, due to the increased distance between the field plates and the 2DEG 230, the field plates 270 and 280 each act as a buffer that helps reduce the voltage present in the channel layer 210 near the position X1. The field plates prevent crowding of the electric field at the edge of the p-gate, and instead of a large peak, the voltage is now spread between consecutive field plates each having a continuously lower electric field peak. Thus, instead of having a single very high electric field peak causing a weak point of the device in location X1 , the electric field is now better distributed without any single fault location.

[0039] That is, while there is indeed an electric field peak 291 at the drain side of the gate contact 260 at position X1, the electric field peak 291 is reduced compared to what it would have been if the HEMT 200 did not include the field plates 270 and 280. This is because, moving leftward from the drain contact 250 toward the gate contact 260, the distance between the 2DEG 230 and the field plate 280 reaches a minimum, and thus a smaller electric field peak 293 is induced in the channel layer 210 at the drain side of the field plate 280 at position X3. Therefore, the voltage in the channel layer 210 below the field plate 280 and moving leftward is reduced. Continuing leftward from the field plate 280, the distance between the 2DEG 230 and the field plate 270 reaches a minimum, and thus another small electric field peak 292 is induced in the channel layer 210 at the drain side of the field plate 270 at position X2. Therefore, the voltage in the channel layer 210 below the field plate 270 and moving to the left decreases even further. Finally, continuing to the left from the field plate 270, the distance between the 2DEG 230 and the gate contact 260 reaches a minimum, and thus a decreasing electric field peak 291 is induced at position X1.

[0040] While field plates 270 and 280 do help reduce the magnitude of the electric field peak that would otherwise have been induced at the drain side of gate contact 260, electric field peak 291 is still significant. Therefore, HEMT 200 would benefit from having electric field peak 291 reduced further.

[0041] This can be accomplished, for example, by adding additional field plates between the gate contact 260 and the drain contact 250. However, the number of field plates that can be added between the gate contact 260 and the drain contact 250 is limited in part by the distance between the gate contact 260 and the drain contact 250. Thus, to add more field plates, the distance between the gate contact 260 and the drain contact 250 will increase, and thus the overall size of the HEMT 200 will increase. Increasing the overall size of the HEMT 200 will result in an increased cost to produce the HEMT 200, since fewer instances of the HEMT 200 can be manufactured on a semiconductor wafer of the same size.

[0042] The inventors have created a HEMT including a hybrid gate contact that allows greater ability to adjust and reduce electric field peaks, particularly at the hybrid gate contact, without increasing the size of the HEMT. In fact, as compared to a HEMT using only an enhanced gate contact 260 Figure 2A Compared to HEMT 200 , a hybrid gate contact according to the principles described herein allows the overall size of the HEMT to be reduced, as well as allowing the HEMT to handle higher voltages and currents.

[0043] Figure 3A3 shows a cross-sectional view of a HEMT 300 having a hybrid gate contact 360 according to the principles described herein. As an example, Figure 3A The HEMT 300 is Figure 1 Therefore, as an example only, Figure 3A The voltage applied to the hybrid gate contact 360 can be applied by the controller 102 via Figure 1 The connector 103 is applied. Figure 3A Below, Figure 3B is corresponding to Figure 3A The electric field profile of HEMT 300. Figure 3A and Figure 3B Align in Figure 3A The electric field at each horizontal position in Figure 3B The electric field plotted immediately below is shown in Figure 2. Also, for consistency purposes, Figure 3A use Figure 2A Coordinate system 201.

[0044] Out of Figure 3A For purposes of the embodiments of the present invention (but not limiting the broader aspects described herein), it is assumed that the channel layer 310, barrier layer 320, 2DEG 330, source contact 340, drain contact 350, and field plates 370 and 380 have the same configuration as described above with reference to Figure 2A The same structures as described with respect to corresponding channel layer 210, barrier layer 220, 2DEG 230, source contact 240, drain contact 250, and field plates 270 and 280. That is, application of the principles described herein allows for greater flexibility in how HEMTs are constructed and sized.

[0045] For purposes of explanation, perpendicular to the epitaxial growth direction, the overall length of the hybrid gate contact 360 is Figure 2A The lengths of the gate contacts 260 are approximately the same. However, Figure 3A The hybrid gate contact 360 is different from Figure 2A 360. That is, the hybrid gate contact 360 includes an enhancement gate portion 362 and a depletion gate portion 363. The hybrid gate contact 360 also includes a p-doped semiconductor portion 361 between the enhancement gate portion 362 and the barrier layer 320 along the epitaxial growth direction. However, there is no such p-doped semiconductor portion below the depletion gate portion 363. Therefore, when zero volts is applied to the hybrid gate contact 360, the p-doped portion 361 causes the 2DEG 330 to be discontinuous only below the enhancement gate portion 362.

[0046] Furthermore, because there is no p-doped semiconductor portion below the depletion gate portion 363, the 2DEG 330 is continuous below the depletion gate portion 363 when zero volts is applied to the hybrid gate contact 360. Thus, the depletion gate portion 363 acts as a buffer to further reduce the electric field peak that would otherwise exist at the drain side of the enhancement gate portion 362. Note, however, that the depletion gate portion 363 is able to reduce the magnitude of the electric field peak at the drain side of the enhancement gate portion 362 without increasing the overall size of the HEMT 300 because the overall length (perpendicular to the epitaxial growth direction) of the hybrid gate contact 360 is 1 / 4 of the total length of the hybrid gate contact 360. Figure 2A The lengths of the gate contacts 260 are approximately the same.

[0047] about Figure 3B , assuming that the HEMT 300 is off so that the source contact 340 and the hybrid gate contact 360 have zero volts applied to them, and there is a large positive voltage at the drain contact 350. For comparison purposes, it is assumed that the large positive voltage present at the drain contact 350 is Figure 2A The same is true of the large positive voltage present at the drain contact 250 of . Figure 2A The field plates 270 and 280 , 370 and 380 each act as a buffer that helps reduce the voltage present in the channel layer 310 approaching the hybrid gate contact 360 from the right side.

[0048] That is, moving leftward from the drain contact 350 toward the hybrid gate contact 360, the distance between the 2DEG 330 and the field plate 380 reaches a minimum, and thus a small electric field peak 393 is induced in the channel layer 310 at the drain side of the field plate 380 at the position X3. Therefore, the voltage in the channel layer 310 below the field plate 380 and moving leftward is reduced. Continuing leftward from the field plate 380, the distance between the 2DEG 330 and the field plate 370 reaches a minimum, and thus another small electric field peak 392 is induced in the channel layer 310 at the drain side of the field plate 370 at the position X2. Therefore, the voltage in the channel layer 310 below the field plate 370 and moving leftward is even further reduced.

[0049] Continuing to the left from the field plate 370, the distance between the 2DEG 330 and the depletion gate portion 363 reaches a minimum, and thus another small electric field peak 391B is induced in the channel layer 310 at the drain side of the depletion gate portion 363 at position X1B. As a result, the voltage in the channel layer 310 below the depletion gate portion 363 and moving to the left decreases even further. Finally, continuing to the left from the depletion portion 363, the voltage in the channel layer 310 has decreased so that at the minimum distance between the 2DEG 330 and the enhancement gate portion 362, as in Figure 2AThe gate contact 260 senses the drain side of Figure 2B Compared to the electric field peak 291 at the drain side of the enhancement gate portion 362, a much smaller electric field peak 391A is induced at the drain side of the enhancement gate portion 362. Therefore, because the overall magnitude of the electric field peak is reduced, particularly at the drain side of the enhancement gate portion 362, the hybrid gate contact 360 according to the principles described herein allows the HEMT 300 to operate at higher voltages and currents without causing damage to the HEMT 300.

[0050] Additionally, while the hybrid gate contact 360 allows for a reduction in the electric field peak, the inventors have also discovered that the use of the hybrid gate contact 360 further reduces the electric field in the channel layer 310 near the drain contact 350. The operation of the HEMT is significantly affected by the magnitude of the electric field peak and the magnitude of the electric field close to the drain contact. For example, a large electric field closer to the drain contact may have a greater adverse effect on the performance of the HEMT.

[0051] Therefore, because the use of hybrid gate contact 360 reduces the electric field in channel layer 310 near drain contact 350, and also because the use of hybrid gate contact 360 significantly reduces the magnitude of the electric field peak in the channel region, as previously described, the overall size of HEMT 300 can be reduced compared to HEMT 200 without hybrid gate contact 360. That is, the distance between drain contact 350 and hybrid gate contact 360 can be reduced while still allowing HEMT 300 to stay within a sufficient performance margin. Therefore, HEMT 300 can be manufactured on the same size semiconductor wafer. Figure 3A More instances of the HEMT 300 can be manufactured, thereby reducing manufacturing costs.

[0052] For the purpose of explanation and comparison, Figure 4 The diagram shows a superimposed Figure 2B and Figure 3B An electric field diagram 400 showing the electric field profile shown in FIG. Figure 2A The electric field profile of the HEMT 200 is shown in dashed line form. Figure 3A The electric field profile of the HEMT 300 is shown in solid line form. In addition, positions X1, X1A, X1B, X2, and X3 are illustrated as vertical dashed lines. Figure 4, the magnitude of the electric field peak 391A at position X1A of HEMT 300 is substantially less than the electric field peak 291 at position X1 of HEMT 200. Further, note that the electric field generally surrounding the drain contact 350 of HEMT 300 (see electric field peak 393 and to the right of the peak) is also less than the electric field surrounding the drain contact 250 of HEMT 200 (see electric field peak 293 and to the right of the peak). Thus, particularly near the hybrid gate contact 360, the use of the hybrid gate contact 360 of HEMT 300 significantly reduces the electric field peak, and generally also reduces the electric field around the drain contact 350. Thus, Figure 3A The hybrid gate contact 360 allows the overall size of the HEMT 300 to be reduced while also allowing the HEMT 300 to operate at higher voltage and current limits.

[0053] The hybrid gate portion 363 can be adjusted to reduce the electric field peak and the overall electric field near the drain contact 350 to a certain extent by changing the size of the hybrid gate contact 360. Figure 3A In the embodiment, the depletion gate portion 363 is thinner than the enhancement gate portion 362 along the epitaxial growth direction.

[0054] Furthermore, perpendicular to the epitaxial growth direction, depletion gate portion 363 is longer than enhancement gate portion 362. Increasing the length of depletion gate portion 363 to some extent also helps provide more robust electric field buffering for enhancement gate portion 362 while keeping the overall length of hybrid gate contact 360 perpendicular to the epitaxial growth direction the same.

[0055] However, while keeping the overall length of the hybrid gate contact 360 the same, increasing the length of the depletion gate portion 363 will mean reducing the length of the enhancement gate portion 362. Reducing the length of the enhancement gate portion 362 will thereby mean reducing the length of the p-doped semiconductor portion 361 perpendicular to the epitaxial growth direction. Reducing the length of the p-doped semiconductor portion 361 will cause a smaller portion of the 2DEG 330 below the enhancement gate portion 362 to be discontinuous when the HEMT 300 is turned off. On the one hand, this allows for reduced on-resistance, which allows the HEMT 300 to operate at higher currents. On the other hand, reducing the portion of the 2DEG 330 that is discontinuous when the HEMT 300 is turned off will also cause the HEMT 300 to have increased leakage current. Taking this concept to its logical end, if the depletion gate portion 363 is long enough so that there is little or no enhancement gate portion 362, the leakage current will be so significant that the HEMT 300 will operate as a depletion-mode HEMT, conducting current when zero volts are applied to the hybrid gate contact 360. Therefore, although the length of the depletion gate portion 363 can be adjusted to some extent in order to adjust the peak value of the electric field in the channel layer 310 , there is a tradeoff between the current carrying capability and the leakage current problem in the HEMT 300 .

[0056] The principles described herein are not limited to Figure 3A of a specific HEMT 300. In fact, there has been Figure 3A The hybrid gate described can be incorporated into many different field effect transistors. In addition, there are advantages that would be beneficial in HEMTs (e.g., Figure 3A Several additional embodiments of a hybrid gate for use in a HEMT 300).

[0057] For comparison purposes, Figure 5A Pictured Figure 2A An example of an enhanced gate contact 260, and Figure 5B Pictured Figure 3A Example of a hybrid gate contact 360 . Figure 5C and Figure 5D Two additional exemplary embodiments of alternative hybrid gate contacts are illustrated, respectively. For simplicity purposes, Figure 5A and Figure 5B The channel layer, barrier layer, 2DEG, gate contact (including Figure 3A The corresponding enhancement / depletion gate portion) and the p-doped semiconductor portion are used with their corresponding Figure 2A and Figure 3A To help illustrate FIG. 5A to FIG. 5D The differences between the various enhancement gate portions and the depletion gate portions, the p-doped semiconductor portions are illustrated as filled with hash marks.

[0058] In addition, FIG. 5A to FIG. 5D In each of the hybrid gate contacts, assuming that the overall length of each hybrid gate contact is the same perpendicular to the epitaxial growth direction. For example, the overall length of each hybrid gate contact perpendicular to the epitaxial growth direction may be 2 μm (micrometer). For example, assuming that Figure 5A The overall length of the enhanced gate contact 260 is 2 μm. In addition, assuming Figure 5B The hybrid gate contact 360 is 2 μm, divided into an enhancement gate portion 362 having a length of 0.8 μm and a depletion gate portion having a length of 1.2 μm.

[0059] Figure 5C A hybrid gate contact 560C is illustrated, disposed above a substrate including a channel layer 510C and a barrier layer 520C. The channel layer 510C and the barrier layer 520C together form a 2DEG 530C within the channel layer 510C. The hybrid gate contact 560C includes two enhancement gate portions 563C and 564C and two depletion gate portions 565C and 566C. The division between each of these gate portions 563C to 566C is illustrated using vertical dashed lines. Below the two enhancement gate portions 563C and 564C are corresponding p-doped semiconductor portions 561C and 562C. Note that the enhancement gate portions 563C and 564C, together with the depletion gate portion 565C, take the same Figure 5B The enhancement gate portion 362 has substantially the same shape as that of the depletion gate portion 566C. Figure 5B The depletion gate portion 363 has substantially the same shape. Alternatively, Figure 5C The hybrid gate contact 560C can be considered as a single enhancement gate portion and a single depletion gate portion, as Figure 5B A hybrid gate contact 360 is shown, but with multiple distinct p-doped semiconductor portions beneath the enhancement gate portion.

[0060] A hybrid gate contact having various enhancement gate portions and depletion gate portions (or multiple p-doped semiconductor portions below the enhancement gate portions), e.g. Figure 5C The hybrid gate contact 560C can help further reduce any large electric field peak at the hybrid gate contact 560C into various smaller electric field peaks. Figure 5C The hybrid gate contact 560C may also allow the overall size of its HEMT to be reduced, and allow its HEMT to operate at higher voltage and current limits.

[0061] Figure 5DA hybrid gate contact 560D is illustrated. The hybrid gate contact 560D is disposed above a substrate including a channel layer 510D and a barrier layer 520D. The channel layer 510D and the barrier layer 520D together form a 2DEG 530D within the channel layer 510D. The hybrid gate contact 560D includes an enhancement gate portion 562D and a depletion gate portion 563D. Below the enhancement gate portion 562D is a p-doped semiconductor portion 561D. The hybrid gate contact 560D takes the same Figure 5B The hybrid gate contact 360 is substantially the same shape, except that the enhancement gate portion 562D and the depletion gate portion 563D are disconnected from each other.

[0062] Disconnecting the enhancement gate portion 562D and the depletion gate portion 563D from each other allows for further manipulation of the electric field. That is, different voltages may be applied to the enhancement gate portion 562D and the depletion gate portion 563D such that the depletion gate portion 563D may be adjusted to act as a stronger buffer or a weaker buffer for the enhancement gate portion 562D. For example, even when the HEMT including the hybrid gate contact 560D is turned off so that zero volts are applied to the enhancement gate portion 562D, a voltage other than zero volts may be applied to the depletion gate portion 563D. The controller 102 may be configured to control the depletion gate portion 563D via the gate contact 560D. Figure 1 The connector 103 of the hybrid gate contact 560D applies such voltages to the enhancement gate portion 562D and the depletion gate portion 563D. In addition, different voltages can be applied to the enhancement gate portion 562D and the depletion gate portion 563D with some time delay (e.g., 20 nanoseconds) between the enhancement gate portion 562D and the depletion gate portion 563D. This may be beneficial, for example, when turning on a HEMT including the hybrid gate contact 560D. Therefore, the hybrid gate contact 560D allows for greater flexibility in manipulating the electric field, thereby further allowing the overall size of the HEMT to be reduced, and allowing the HEMT to operate at higher voltage and current limits.

[0063] Thus, what has been described is a circuit for controlling a HEMT. The HEMT includes a hybrid gate contact that includes an enhancement gate portion and a depletion gate portion. The circuit further includes a controller that can apply various voltages to the enhancement gate portion and the depletion gate portion. The use of the hybrid gate contact allows for a greater ability to adjust and reduce electric field peaks, thereby allowing the overall size of the HEMT to be reduced, and / or allowing the HEMT to handle higher voltages and currents, as compared to a HEMT having only an enhancement gate.

[0064] Text support part

[0065] Clause 1. A circuit comprising a high electron mobility transistor and a controller, wherein the high electron mobility transistor comprises: an epitaxial layer epitaxially grown on a substrate along an epitaxial growth direction, the epitaxial layer comprising a channel semiconductor layer and a barrier semiconductor layer epitaxially grown on the channel semiconductor layer, the interface between the barrier semiconductor layer and the channel semiconductor layer defining a heterojunction inducing a two-dimensional electron gas (2DEG) in the channel semiconductor layer, the 2DEG extending perpendicular to the epitaxial growth direction; a source contact, the source contact being in conductive contact with a first portion of the 2DEG; a drain contact, the drain contact being in conductive contact with a second portion of the 2DEG; a gate contact, The long direction is arranged above the barrier semiconductor layer and is arranged between the drain contact and the source contact in the direction perpendicular to the epitaxial growth direction, the gate contact includes an enhancement gate part and a depletion gate part, the depletion gate part is arranged between the enhancement gate part and the drain contact in the direction perpendicular to the epitaxial growth direction; and a p-doped semiconductor part, between the enhancement gate part and the barrier semiconductor layer along the epitaxial growth direction, so that when zero volts is applied to the enhancement gate part, the 2DEG is discontinuous below the enhancement gate part, and the depletion gate part is configured so that when zero volts is applied to the depletion gate part, the 2DEG is continuous below the depletion gate part.

[0066] Item 2. The circuit of Item 1, wherein the enhancement gate portion and the depletion gate portion are disconnected.

[0067] Item 3. The circuit of Item 2, the controller configured to at least sometimes apply a voltage to the enhancement gate portion that is different than a voltage applied to the depletion gate portion.

[0068] Item 4. The circuit of Item 3, the controller configured to apply at least a turn-on voltage to the enhancement gate portion to thereby turn on the high electron mobility transistor, and further configured to apply a voltage to the depletion gate portion within a specific delay after applying the turn-on voltage to the enhancement gate portion.

[0069] Clause 5. The circuit of clause 1, wherein the specified delay is 20 nanoseconds or less.

[0070] Item 6. The circuit of Item 1, wherein the enhancement gate portion and the depletion gate portion are electrically connected together.

[0071] Item 7. The circuit of Item 6, the controller configured to apply at least a turn-on voltage to the enhancement gate portion to thereby turn on the high electron mobility transistor, the controller further configured to apply a turn-on voltage to the connected depletion gate portion.

[0072] Item 8. The circuit of Item 1, wherein the thickness of the enhancement gate portion is greater than the thickness of the depletion gate portion along the epitaxial growth direction.

[0073] Clause 9. The circuit of clause 1, wherein the length of the enhancement gate portion is shorter than the length of the depletion gate portion in a direction perpendicular to the epitaxial growth direction.

[0074] Item 10. The circuit of Item 1, wherein the channel layer is a gallium nitride (GaN) channel layer.

[0075] Clause 11. The circuit of clause 1, wherein the barrier layer is an aluminum gallium nitride (AlGaN) layer. Although the subject matter has been described in language specific to structural features and / or methodological acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the described features or acts described above or the order of acts described above. Rather, the described features and acts are disclosed as example forms of implementing the claims.

[0076] Without departing from the basic characteristics of the present disclosure, the present disclosure may be embodied in other specific forms. The described embodiments should be considered in all respects as merely illustrative and not restrictive. All changes that fall within the meaning and range of equivalents of the claims are included within their scope.

[0077] When introducing elements in the appended claims, the articles “a,” “an,” “said,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Claims

1. A circuit comprising a high electron mobility transistor and a controller, wherein the high electron mobility transistor comprises: An epitaxial layer is epitaxially grown on a substrate along an epitaxial growth direction, the epitaxial layer comprising a channel semiconductor layer and a barrier semiconductor layer epitaxially grown on the channel semiconductor layer, an interface between the barrier semiconductor layer and the channel semiconductor layer defines a heterojunction that induces a two-dimensional electron gas (2DEG) in the channel semiconductor layer, and the 2DEG extends perpendicular to the epitaxial growth direction; a source contact in conductive contact with the first portion of the 2DEG; a drain contact in conductive contact with a second portion of the 2DEG; a gate contact, arranged above the barrier semiconductor layer along the epitaxial growth direction and arranged between the drain contact and the source contact in a direction perpendicular to the epitaxial growth direction, the gate contact comprising an enhancement gate portion and a depletion gate portion, the depletion gate portion being arranged between the enhancement gate portion and the drain contact in a direction perpendicular to the epitaxial growth direction; and A p-doped semiconductor portion is disposed between the enhancement gate portion and the barrier semiconductor layer along the epitaxial growth direction, so that when zero volt is applied to the enhancement gate portion, the 2DEG is discontinuous below the enhancement gate portion, and the depletion gate portion is configured so that when zero volt is applied to the depletion gate portion, the 2DEG is continuous below the depletion gate portion.

2. The circuit of claim 1, wherein the enhancement gate portion and the depletion gate portion are disconnected.

3. The circuit of claim 2, the controller configured to apply a voltage to the enhancement gate portion that is different from a voltage applied to the depletion gate portion at least sometimes.

4. The circuit of claim 3 , the controller being configured to apply at least a turn-on voltage to the enhancement gate portion to thereby turn on the high electron mobility transistor, and further configured to apply a voltage to the depletion gate portion within a certain delay after applying the turn-on voltage to the enhancement gate portion. The circuit of claim 1 , wherein the specific delay is 20 nanoseconds or less.

6. The circuit of claim 1, the enhancement gate portion and the depletion gate portion being electrically connected together.

7. The circuit of claim 6, the controller being configured to apply at least a turn-on voltage to the enhancement gate portion to thereby turn on the high electron mobility transistor, the controller being further configured to apply the turn-on voltage to the connected depletion gate portion. 8 . The circuit of claim 1 , wherein along the epitaxial growth direction, the thickness of the enhancement gate portion is greater than the thickness of the depletion gate portion.

9. The circuit of claim 1, wherein the enhancement gate portion has a length shorter than the depletion gate portion in a direction perpendicular to the epitaxial growth direction.

10. The circuit of claim 1, the channel layer being a gallium nitride (GaN) channel layer.

11. The circuit of claim 1, the barrier layer being an aluminum gallium nitride (AlGaN) layer.

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