CROSS REFERENCE
The present application is based on, and claims priority from, Chinese application number 201611095490.3, filed on Dec. 2, 2016, the disclosure of which is hereby incorporated by reference herein in its entirety.
TECHNICAL FIELD
The present invention relates to the technical field of semiconductor switches, more particularly, to a GaN-Based bidirectional switch device.
BACKGROUND
Bidirectional switches, capable of conducting currents and blocking voltages of both polarities, are wildly used in many applications, such as compact motor drives, aircrafts, AC power supply units, electric propulsion of ships, and electric cars, Conventional high-voltage bidirectional switches are constructed by two Si-based insulated gate bipolar translators (IGBTs) connected in reversed series and two power diodes, as shown in FIG. 1(a). In this configuration, the current flows through two different devices, this will lead to a high on-state voltage drop, making the bidirectional switches lose more power. To reduce the on-state voltage drop of bidirectional switches and improve efficiency, controllable switches with high reverse blocking (RB) capability, such as RB-IGBTs, have been developed in recent years. The controllable switches with high reverse blocking (RB) capability are as shown in FIG. 1(b). In this new configuration, the current only flows through a single device, and shorter current path will be beneficial for reducing the on-state voltage drop and lowering on-state loss. But the new configuration goes against chip-area utilization, because only one of the two current channels can conduct currents in the bidirectional conducting mode. In order to cut the cost of bidirectional switches or improve the chip-area utilization, a monolithic bidirectional switch with only One channel and two gates is proposed, as shown in FIG. 1(c). The monolithic bidirectional switch has only one conductive channel, two currents of different direction flow through one channel, so the chip-area utilization is improved. The on-state voltage drop is reduced when current flows through only one channel.
Gallium nitride is one of the representatives of the third generation of wide bandgap semiconductors, which is attracting widespread attention. The superior performance of Gallium nitride mainly lies in high critical breakdown electric field (˜3.5×106 V/cm) high electron mobility (˜2000 cm2/V·s.), high concentration of two-dimensional electron gas (2 DEG) (˜1013 cm−2), and high temperature working ability. Forbidden band width of GaN materials is up to 3.4 eV, which is 3 times the forbidden band width of Si materials and 2.5 times the forbidden band width of GaA materials. Intrinsic carrier concentration of the semiconductor materials increases exponentially with the forbidden band width and temperature. Therefore, up to a certain temperature range, more the semiconductor materials forbidden band width, smaller is the intrinsic carrier concentration. This can make the device to have a very low leakage current. In addition, gallium nitride (GaN) is stable in chemical properties, has high temperature resistance, and corrosion resistance and has inherent advantages in high frequency, high power, and anti-radiation application. The high electron migration rate transistor (HEMT) based on AlGaN/GaN heterojunction (or heterojunction effect transistor HFET, modulation doped field effect transistor MODFET) has been widely used in the semiconductor field. This kind of device has the characteristics of high reverse blocking voltage, low positive on-state resistance, and high working frequency so it can make the semiconductor devices satisfy the requirements of more powerful, smaller volume and higher frequency.
In recent years, in order to achieve low power efficient bidirectional switch, the researchers proposed GaN HEMT devices with reverse conducting type (RC-MISHEMT), but from the above analysis, the bidirectional switch based on reverse conducting type large on-state voltage drop and on-state loss. In order to further reduce the bidirectional on-state voltage drop and on-state loss and improve the switching efficiency of the switch, the bidirectional switch device is very necessary. Therefore, the invention proposes the GaN-based bidirectional switch device, the structure of which is shown in FIG. 2. Each insulated gate structure near schottky-contact controls the band structure of the schottky-contact to change the working state of the device, realizing the bidirectional switch's ability of bidirectional conducting and blocking. Due to the only presence of schottky in this invention, no heavy element such as gold is necessary, so the present invention is compatible with traditional CMOS technology.
SUMMARY OF INVENTION
In view of the main indexes of high-efficiency power switching devices (chip area utilization, on-state resistance, reverse resistance, and power consumption), the GaN-based bidirectional switch device is proposed. The present invention has the advantages of high utilization of chip area, low on-state resistance, high reverse blocking ability, and low power consumption, especially in matrix converters.
The technical solution of the present invention is as below.
A GaN-based bidirectional switch device comprises a substrate 1, a GaN buffer layer 2 and a MGaN layer 3. The GaN buffer layer 2 and the MGaN layer 3 form a heterojunction. A Schottky source electrode is located at one end of the device, and a Schottky drain electrode is located at the other end of the device. The Schottky source electrode and the Schottky drain electrode are symmetrical with respect to a median vertical line of the device. The Schottky source electrode has a grooved schottky structure, which comprises a deeply recessed trench formed by etching the GaN buffer layer 2, and a source schottky-contact electrode 9 contacting with the GaN buffer layer 2 and covering the deeply recessed trench. The side of the source schottky-contact electrode 9 contacts the MGaN layer 3. The Schottky drain electrode has a grooved schottky structure comprising a recessed trench which is formed by etching the GaN butler layer 2 and a drain schottky-contact electrode 10 contacting with the GaN buffer layer 2 and covering the deeply recessed trench. The side of the drain schottky-contact electrode 10 contacts the MGaN layer 3. The upper layer of the MGaN layer 3 contacting the source schottky-contact electrode 9 has a first insulated gate structure. The upper layer of the MGaN layer 3 contacting the drain schottky-contact electrode 10 has a second insulated gate structure. The first ins dated gate structure and the second insulated gate structure are symmetrical about the median of the device. The first insulated gate structure comprises a recessed trench formed by etching the MGaN layer 3, an insulated gate dielectric 6 covering the recessed trench, and a first metal gate electrode 7 covering the gate medium. The second insulated gate structure comprises a recessed trench which is formed by etching the MGaN the insulated rate dielectric 6 which covers the recessed trench, and the first metal gate electrode 7 which covers the gate medium. The M is a III group element excluding Ga.
Particularly, the depth that source schottky-contact electrode 9 and the drain schottky-contact electrode 10 are embedded in the GaN buffer layer 2 is 0.5 um.
Particularly, the material of the insulated gate dielectric 6 is SiO2, SiN4, AlN, Al2O3, MgO, or Sc2O3.
It is important to note that the ability to block off the device can be increased by increasing the depth that the insulated gate electrode is embedded in the MGaN layer's surface.
The benefit of the present invention is that, compared with the traditional structure, the device of the present invention has the advantages of high utilization ratio chip area, low on-state resistance, high reverse blocking ability, and low power consumption, especially in matrix converters. Due to the only presence of schottky in this invention, no heavy elements such as gold is required, so the present invert is compatible with traditional CMOS technology.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the structure of the traditional bidirectional switch device, wherein (a) is the series type, (b) is the parallel type, and (c) is the device type;
FIG. 2 shows the structure of the present invention;
FIG. 3 shows working principle of the present invention;
FIG. 4 shows the bidirectional conducting characteristics of GaN-based bidirectional switch of the present invention;
FIG. 5 shows the bidirectional blocking characteristics of GaN-based bidirectional switch of the present invention;
FIG. 6 shows the substrate of the present invention;
FIG. 7 shows the structure diagram of the barrier layer to the GaN buffer layer in the process flow of the device manufacturing process.
FIG. 8 a schematic diagram of the structure of the source extreme schottky-contact and the leaky schottky-contact in the manufacturing process of the invention.
FIG. 9 shows the schematic diagram of the structure of the first and second partially recessed shallow trench in the manufacturing process of the device.
FIG. 10 is a schematic diagram of the post-deposition insulation layer in the manufacturing process of the device.
FIG. 11 shows the schematic diagram of the metal back in the first partially recessed shallow trench and the second partially recessed shallow trench in the manufacturing process of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The technical scheme of the invention is described in detail below.
As shown in FIG. 2, the GaN-Based bidirectional switch device comprises a substrate 1, a GaN buffer layer 2, and a MGaN layer 3. The GaN buffer layer 2 and the MGaN layer 3 form a heterojunction. A Schottky source electrode is located at one end of the device, and a Schottky drain electrode is located at another end of the device. The Schottky source electrode and the Schottky drain electrode are symmetrical with respect to a median vertical line of the device. The Schottky source electrode has a grooved schottky structure, which comprises a recessed trench formed by etching the GaN buffer layer 2, and a source schottky-contact electrode 9 contacting with the GaN buffer layer 2 and covering the recessed trench. The side of the source schottky-contact electrode 9 contacts the MGaN layer 3. The Schottky drain electrode has a grooved schottky structure, which comprises a recessed trench formed by etching the GaN buffer layer 2, and a drain schottky-contact electrode 10 contacting with the GaN buffer layer 2 and covering the recessed trench. The side of the drain schottky-contact electrode 10 contacts the MGaN layer 3. The upper layer of the MGaN layer 3 contacting the source schottky-contact electrode 9 has a first insulated gate structure. The upper layer of the MGaN layer 3 contacting the drain schottky-contact electrode 10 has a second insulated gate structure. The first insulated gate structure and the second insulated gate structure are symmetrical about the median of the device. The first insulated gate structure comprises a recessed trench formed by etching the MGaN layer 3, an insulated gate dielectric 6 covering the recessed trench, and a first metal gate electrode 7 covering the gate medium. The second insulated gate structure comprises a recessed trench which is formed by etching the MGaN layer 3, the insulated gate dielectric 6 covering the recessed trench, and the first metal gate electrode 7 covering the gate medium. The M is a III group element excluding Ga.
The bidirectional switches based on the reverse conducting devices have large on-state voltage drop and on-stale loss. In addition, the utilization rate of the chip's area of the bidirectional switch based on the reverse blocking device is low. The invention proposes the GaN-Based bidirectional switch device (as FIG. 2). The source and drain of this device are schottky-contacted. At the same time, the AlGaN layer near the source and drain structure has a gate structure. This device has no Ohmic-contact and no requirement for using heavy metal and can be compatible with CMOS process. Each insulated gate structure near schottky-contact controls the band structure of the schottky-contact to change the working state of the device, realizing the bidirectional switch's ability of bidirectional conducting and blocking. At the same time, there is only one conductive channel in the device, and the chip area has a high utilization rate. In addition, the on-state resistance, leakage current and on-state voltage drop can be controlled by the gate, which controls the on-state resistance and the on-state voltage drop by controlling the thickness of AlGaN barrier layer under the gate structure TG, the power function of gate metal Wm, and the length of the groove MIS structure. The blocking ability of the GaN-Based bidirectional switch device is decided by both gate structure and schottky structure. The device has a better reverse blocking ability when the thickness of the AlGaN barrier layer under the gate structure is relatively thin and the source schottky-contacting harrier is relatively large. However, this can cause the increase of on-state resistance and on-state voltage drop.
It is important to note that the design process of the invention embodies the following details.
- 1. The AlGaN harrier layer of source and drain is etched as far as possible.
- 2. A passivation layer is deposited on the surface of AlGaN layer to further reduce leakage and improve performance.
- 3. The schottky-contact and the structure of insulated gate are separated by insulating medium, and the quality of media directly affects the performance of the device.
The basic working principle of this device is as below.
Firstly, each insulated gate structure near schottky-contact controls the band structure of the schottky-contact to change the working state of the device, realizing the bidirectional switch's ability of bidirectional conducting and blocking. When the gate is applied with a positive voltage, the thickness of the harrier near schottky is thinned (FIG. 3), the probability of the electron tunneling increases, and thus the device can have the current characteristics similar to ohm's contact. When the gate is applied with a negative voltage, the thickness of the harrier near schottky becomes thicker, the probability of electron tunneling is reduced, and the electron is almost impossible to pass the barrier. Therefore, the device can realize the blocking ability. When only one gate is applied with a positive voltage, the bidirectional switch can only be used in one direction to conduct the rent, and in the other direction it shows the ability of blocking. The invention uses the schottky junction and insulated gate structure to suppress the reverse leakage of the device. The invention increases the depletion capacity of the carrier under the gate by reducing the thickness of the barrier layer under the insulated gate. The simulation circuit diagram shown in FIG. 5. The blocking mechanism of the bidirectional switch can be explained as follows. When the voltage is low, the schottky-contacting barrier of source and drain blocks the current. When the voltage increases, the carriers at the bottom of the gate near schottky begins to run out. When the carriers under the gate get completely exhausted, the carriers cannot pass through the gate channel, then the insulated gate blocks current. Reducing the thickness of the barrier layer can increase the blocking ability of the device. FIG. 4 shows the bidirectional conduction characteristics of the present GaN-based bidirectional switch. FIG. 5 shows the bidirectional blocking characteristics of the based bidirectional switch.
The device of this invention is compatible with the traditional CMOS process and can be made by using the traditional CMOS process line. What needs to be specified specifically is the following.
- 1. The groove of drain electrode and source electrode must be extended to GaN2.
- 2. The material of the insulated gate dielectric 6 is SiO2, SiN4, AlN, Al2O3, MgO, or Sc2O3.
- 3. The first partially recessed shallow trench 4 must be near the source schottky-contacts, and the second partially recessed shallow trench 5 must be near the drain Schottky-contacts.
- 4. The blocking ability of the device can be increased by increasing the depth of the first partially recessed shallow trench 4 and the second partially recessed shallow trench 5.
In the present invention, the following two schemes can be used to prepare the insulating medium materials.
- (a) The dielectric material (such as Al2O3, HfO2 and TiO2) is prepared by atomic layer deposition (ALD). The film grown by ALD is self-limiting, and the thickness and chemical composition of the film can be accurately controlled. The deposited film has good uniformity and conformal properties. The composite laminates, such as HfO2/Al2O3, etc, should be considered.
- (b) A variety of single-layer, multi-layer, and various laminated structures (such as Ga2O3, Al2O3, AlGaO or AlGaO/Al2O3) are prepared though MOCVD equipment to prepare high-performance insulating grid media. MOCVD method has the advantages of dense film forming state of dielectric material, accurate thickness control, easily forming hybrid film, and good repeatability of multilayer film, especially the large controlled space in interface state controlling.
The manufacturing process of the invention is shown in FIG. 6-FIG. 11 and mainly comprises the following steps.
FIG. 6 shows the preparation of heterojunction with substrate and harrier layer. FIG. 7 shows etching barrier layer to GaN buffer layer in source and drain contact. FIG. 8 shows passivating opening and producing source and drain schottky-contact metal. FIGS. 9 and 10 show providing openings in the first recessed trench gate and the second recessed trench gate and depositing insulating dielectric. FIG. 11 shows deposition of gate metal.
Device simulation software Sentaurus is used to primarily simulate and analyze the structure of the invention. In this simulation, gate length is 1 μm, the medium thickness between the gate and source is 10 nm, the distance between the two gates is 10 μm, the width of the gate is 10000 μm, the thickness of the GaN buffer layer is 3 μm, the thickness of Al0.26 Ga0.74 N barrier layer is 25 nm, and the gate metal working function is 4.5 eV The schottky barrier of source and drain are 1.0 eV.
It can be seen from the curve of the bidirectional conducting characteristics (FIG. 4), when the gate voltage is 10 V and the current is 5 A, the on-state resistance of the device is 0.997 mΩ·cm2. FIG. 5 is the bidirectional blocking characteristic curve of the bidirectional switch device. When the gate voltage is 0V and the drain voltage is ±500 V, the leakage current is 10 μA. This shows that the device has bidirectional blocking capability. Through the above simulation, the excellent performance of the invention is verified.
Patent Application
20180158936
