GaN field effect transistor with ferroelectric polarization coupling field plate

Abstract

The invention discloses a GaN field effect transistor with a ferroelectric polarization coupling field plate. The transistor comprises a GaN epitaxial structure, source electrode metal, drain electrode metal, a source-drain protection medium, grid electrode metal and the ferroelectric polarization coupling field plate, wherein the source electrode metal, the drain electrode metal, the source-drain protection medium and the grid electrode metal are prepared on the GaN epitaxial structure; the GaN epitaxial structure sequentially comprises a substrate, a nucleating layer, a high-resistance buffer layer, a channel layer and a barrier layer from bottom to top, the ferroelectric polarization coupling field plate is located between the gate metal and the drain metal and does not make contact with the gate metal and the drain metal, and the ferroelectric polarization coupling field plate can partially cover the gate metal after the passivation medium grows on the gate. And the ferroelectric polarization coupling field plate is made of a ferroelectric material and has a spontaneous polarization characteristic. Through the ferroelectric polarization coupling field plate characteristic of the ferroelectric material of the device, the electric field distribution in the GaN channel is regulated and controlled by using the induced electric field of the electric dipole, so that the parasitic and breakdown characteristics of the device are regulated and controlled.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ferroelectric materials and the field of third-generation semiconductor microwave and millimeter wave devices, and in particular to a GaN field effect transistor with a ferroelectric polarization coupled field plate. BACKGROUND

[0002] Third-generation semiconductor GaN devices have a larger band gap and higher operating voltage, and have broad application prospects in the field of microwave and millimeter wave chips. Due to the converse piezoelectric effect of the AlGaN / GaN interface, there is a two-dimensional electron gas in the GaN channel, so that the potential barrier generated by the gate of the device has a control effect on the two-dimensional electron gas in the channel, i.e. a voltage-controlled current device. Due to the modulation effect of the gate voltage on the channel current, field effect transistor devices are widely used in active devices such as radio frequency switches and power amplifiers. The modulation mode of the traditional field effect transistor is a voltage-controlled current device, i.e. the change of the gate voltage can control the size of the channel current.

[0003] As the operating voltage of GaN devices increases, the electric field under the gate is too concentrated, which can easily damage the device due to excessive local electric stress. The presence of a field plate can be used to adjust the electric field distribution, thereby improving some characteristics. For example, under high voltage conditions, the electric field will concentrate in a certain area, leading to an increase in breakdown or leakage current, and the field plate can disperse the electric field, reduce the peak electric field strength, and thus improve the breakdown voltage. In power devices, the field plate is used to expand the depletion region, uniformize the electric field, and improve the withstand voltage capability. The field plate can be located near the gate, or connected to the source or the drain.

[0004] The field plate in the traditional field effect transistor is formed by using Ti, Pt, Au or a combination of materials. The typical mode of field plate regulation is that the field plate is connected to the source and is applied above the gate or on the side of the gate-drain, thereby forming an adjusted electric field between the drain and the field plate. However, the traditional field plate metal does not have spontaneous polarization and does not generate electric dipoles, i.e. there is no built-in electric field. In the absence of an electric field, the field plate has a weak regulating effect on the internal electric field of the channel. If a ferroelectric polarization film is used as the field plate of the field effect transistor device, due to the polarization coupling effect of the ferroelectric polarization film, it will have a modulating effect on the two-dimensional electron gas in the channel. The ferroelectric polarization film can generate spontaneous polarization inside the film. The ferroelectric polarization film can also control the direction of the polarization electric field inside the film through an electric field. Due to the existence of the hysteresis loop of the ferroelectric polarization film, there is an internal built-in electric field in the film, and at the same time, due to the polarization coupling effect of the ferroelectric polarization film, a coupling electric field is generated in the channel below the ferroelectric polarization field plate. Therefore, by using the ferroelectric polarization coupled field plate, the electric field distribution below the channel is modulated, thereby affecting the electric field distribution of the device and improving the breakdown characteristics. SUMMARY

[0005] The technical problem solved by the present application: In view of the problems in the prior art, the present application provides a GaN field effect transistor with a ferroelectric polarization coupled field plate, which uses a ferroelectric polarization film as a field plate and uses the induced electric field of its electric dipole to strengthen the regulation of the channel electric field.

[0006] Technical scheme: A GaN field effect transistor with a ferroelectric polarization coupled field plate comprises a GaN epitaxial structure and a source metal, a drain metal, a source-drain protection medium, a gate metal and a ferroelectric polarization coupled field plate prepared on the GaN epitaxial structure; the GaN epitaxial structure comprises, from bottom to top, a substrate, a nucleation layer and a high-resistance buffer layer, a channel layer and a barrier layer; the ferroelectric polarization coupled field plate is located between the gate metal and the drain metal and does not contact both.

[0007] The ferroelectric polarization coupled field plate comprises, from bottom to top, a metal primer layer and a ferroelectric material layer, the ferroelectric material has ferroelectric polarization characteristics, and the metal primer layer is prepared on the source-drain protection medium; the ferroelectric polarization coupled field plate can be a separate structure without electricity or connected with the source metal.

[0008] The metal material in the metal primer layer is at least one of Cr, Mu, Al, Ta, Ti, Pt, Pd, Ru and Au; the ferroelectric material in the ferroelectric material layer is at least one of a perovskite-type ferroelectric material, an acid lithium-type ferroelectric body, a bronze-type ferroelectric body, a bismuth-layered perovskite structure ferroelectric body, a two-dimensional AB-type layered stacking material and a multi-domain ferroelectric material.

[0009] The perovskite-type ferroelectric material comprises BaTiO3, PbTiO3, PbTiZrO3 and KNbO3; the acid lithium-type ferroelectric body comprises LiNbO3, LiTaO3 and BiFeO3; the bronze-type ferroelectric body comprises PbTa2O6, PbNb2O6 and Ba2Sr3Nb 10 O 30 ; the bismuth-layered perovskite structure ferroelectric body comprises SrBi2Ta2O9 ferroelectric material; the two-dimensional AB-type layered stacking material comprises BN, AlN, ZnO, MoS2 and GaSe; and the multi-domain ferroelectric material is Hf x Zr 1-x O2.

[0010] The GaN epitaxial structure further comprises an AlGaN back barrier layer, and the AlGaN back barrier layer is arranged between the channel layer and the nucleation layer and the high-resistance buffer layer.

[0011] The GaN epitaxial structure further comprises an AlN insertion layer, and the AlN insertion layer is arranged between the channel layer and the barrier layer.

[0012] The GaN epitaxial structure further includes a GaN cap layer, which is disposed on the upper surface of the barrier layer.

[0013] The source / drain protection medium is at least one of SiN, SiO2, or metal oxides such as MgO, Al2O3, HfO2, and ZrO.

[0014] The substrate is any one of Si single crystal, sapphire, high-purity semi-insulating SiC, GaN single crystal, and diamond substrate.

[0015] The nucleation layer and the high-resistivity buffer layer are at least one of AlGaN, iron-doped GaN, vanadium-doped GaN, AlN, AlN / GaN superlattice, and AlGaN / GaN superlattice materials.

[0016] The channel layer is one of GaN or InGaN materials.

[0017] The barrier layer is any one of AlGaN, AlInN, AlN, AlInGaN, and P-type GaN.

[0018] The substrate has a thickness of 400 μm-1500 μm, the nucleation layer and high-resistivity buffer layer have a thickness of 1500 nm, the channel layer has a thickness of 200 nm, the barrier layer has a thickness of 20 nm, the gate metal has a thickness of 200-1000 nm, and the ferroelectric polarization coupling field plate has a thickness of 70-250 nm.

[0019] Beneficial effects:

[0020] 1. This invention employs a ferroelectric polarization coupling field plate structure. Ferroelectric materials possess ferroelectric polarization characteristics and can generate ferroelectric polarization coupling. This structure is the first to introduce a ferroelectric polarization coupling field plate structure into a field-effect transistor.

[0021] 2. The ferroelectric polarization coupling field plate of the present invention has spontaneous polarization characteristics, which generates electric dipoles to establish a built-in electric field and simultaneously generates a coupling electric field in the channel; thereby regulating the electric field distribution in the channel and improving the breakdown field strength of the device. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a GaN epitaxial structure.

[0023] Figure 2 This is a cross-sectional schematic diagram of the source / drain metals and growth protective medium fabricated on a GaN epitaxial structure.

[0024] Figure 3 A schematic cross-sectional view of the gate structure fabricated on the source / drain metal and the growth protective medium.

[0025] Figure 4 This invention provides a schematic diagram of a GaN field-effect transistor structure with a ferroelectric polarization coupling field plate.

[0026] In the diagram, the numbers represent the following: 101. Substrate; 102. Nucleation layer and high-resistivity buffer layer; 103. Channel layer; 104. Barrier layer; 105. AlGaN back barrier layer; 106. AlN insertion layer; 107. GaN cap layer; 108. GaN epitaxial structure; 201. Source metal; 202. Source / drain protection dielectric; 203. Gate metal; 204. Ferroelectric polarization coupling field plate; 205. Drain metal; 206. Metal underlayer; 207. Ferroelectric material layer. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0028] This invention provides a GaN field-effect transistor with a ferroelectric polarization coupling field plate, see [link to relevant documentation]. Figure 4 The system includes a GaN epitaxial structure 108 and source metal 201, drain metal 205, source-drain protection dielectric 202, gate metal 203, and ferroelectric polarization coupling field plate 204 fabricated on the GaN epitaxial structure 108. The gate metal 203 is located between the source metal 201 and the drain metal 205. The source-drain protection dielectric 202 is disposed on the source metal 201 and the drain metal 205, between the source metal 201 and the gate metal 203, and between the gate metal 203 and the drain metal 205, respectively, to protect the source metal 201, the drain metal 205, and the barrier layer 104 on the GaN epitaxial structure 108. The GaN epitaxial structure 108 includes, from bottom to top, a substrate 101, a nucleation layer and a high-resistivity buffer layer 102, a channel layer 103, and a barrier layer 104. The ferroelectric polarization coupling field plate 204 is disposed above the source-drain protection dielectric 202, located between the gate metal 203 and the drain metal 205, and does not contact either of them. The ferroelectric polarization coupling field plate 204 can be a standalone structure without power, or it can be connected to the source metal 201 or partially cover the gate metal 203 (without direct contact with the gate metal 203).

[0029] like Figure 1As shown, the GaN epitaxial structure 108 includes a substrate 101 and a nucleation layer, a high-resistivity buffer layer 102, a channel layer 103, and a barrier layer 104 sequentially grown on the substrate 101. The substrate 101 is any one of Si single crystal, sapphire, AlN, SiC, GaN single crystal, or diamond substrate. The nucleation layer and high-resistivity buffer layer 102 are composed of one or more of AlGaN, iron-doped GaN, vanadium-doped GaN, AlN, AlN / GaN superlattice, and AlGaN / GaN superlattice materials. The channel layer 103 is one of GaN or InGaN materials. The barrier layer 104 is any one of AlGaN, AlInN, AlN, and AlInGaN. The thickness of each layer can be as follows: substrate 101 400 μm-1500 μm, nucleation layer and high-resistivity buffer layer 102 1500 nm, channel layer 103 200 nm, and barrier layer 104 20 nm. The thickness of each layer can be adjusted according to the specific device requirements. When the barrier layer 104 is AlGaN, the specific Al content can be determined by the device application requirements, such as 15% to 45%. In addition, for different application environments, other layers can be selectively inserted to meet the requirements of breakdown voltage, mobility, and other characteristics. For example, an AlGaN back barrier layer 105 can be inserted between the channel layer 103 and the nucleation layer and high-resistivity buffer layer 102; an AlN insertion layer 106 can be inserted between the channel layer 103 and the barrier layer 104; and a GaN cap layer 107 can be grown on the surface of the barrier layer 104. Since the typical epitaxial layer of the present invention includes a substrate 101, a nucleation layer and a high-resistivity buffer layer 102, a channel layer 103, and a barrier layer 104, other insertion layers are not discussed for the time being, and whether or not the selective structure is prepared does not affect the implementation of the GaN field-effect transistor of the ferroelectric polarization coupling field plate of the present invention.

[0030] like Figure 2 As shown, source metal 201 and drain metal 205 are fabricated on the GaN epitaxial structure 108, and source / drain protection dielectric 202 is grown on the source metal 201, drain metal 205, and the upper surface of the GaN epitaxial structure 108. The source and drain are formed by fabricating ohmic contact metals. Specific ohmic contact processes and ohmic contact metals are not within the scope of this invention and are therefore not limited. Other structures and processes may be involved in microwave and millimeter-wave monolithic integrated circuits, such as active region isolation, resistor fabrication, capacitor and microstrip fabrication, etc. Since these are not the focus of this invention, their fabrication methods and sequences are not limited. The source / drain protection dielectric 202 also protects the surface of the barrier layer 104 of the active region. Photolithography is then performed on the isolation region, followed by implantation isolation. The source / drain protection dielectric 202 is any one or a combination of SiN, SiO2, or metal oxides MgO, Al2O3, HfO2, and ZrO. In one preferred embodiment of this invention, the source / drain protection dielectric 202 is SiN.

[0031] like Figure 3 As shown, the gate metal 203 of the device is fabricated through processes such as photolithography, etching, electron beam evaporation, and sputtering. The specific fabrication method is not within the scope of this invention and is therefore not limited. Generally, after the gate metal 203 is fabricated, a gate protection medium needs to be grown to protect it. The gate protection medium is generally SiN, but can also be SiO or other media, without limitation. After the gate metal 203 is fabricated, a ferroelectric polarization coupling field plate 204 is fabricated through photolithography, electron beam evaporation, sputtering, and lift-off processes. This field plate can be structurally independent or connected to the source. The ferroelectric polarization coupling field plate 204 consists of a metal underlayer 206 and a ferroelectric material layer 207 from bottom to top. The bottom metal material can increase its adhesion to the source / drain protection medium 202. Specifically, the material can be any one or a combination of Cr, Mu, Al, Ta, Ti, Pt, Pd, Ru, and Au metals. The upper ferroelectric material can be perovskite ferroelectric material (BaTiO3, PbTiO3, PbTiZrO3, KNbO3), lithium oxide ferroelectric material (LiNbO3, LiTaO3, BiFeO3), or bronze mineral ferroelectric material (PbTa2O6, PbNb2O6, Ba2Sr3Nb). 10 O 30 ); Bismuth layered perovskite ferroelectric materials (SrBi2Ta2O9 ferroelectric materials), two-dimensional AB-type layered stacked materials (BN, AlN, ZnO, MoS2, GaSe), multi-domain ferroelectric materials (Hf x Zr 1-x Any one or combination of O2.

[0032] In one preferred embodiment, the gate metal 203 is a combination of Ti, Pt, and Au, with a total thickness between 200 and 1000 nm. In the ferroelectric coupling field plate, the bottom layer 206 is Ti metal, and the ferroelectric material layer 207 (ferroelectric polarization film) is perovskite-type ferroelectric material BaTiO3. The thickness of the Ti metal is 50 nm, and the thickness of the perovskite-type ferroelectric material BaTiO3 is 20 nm to 200 nm. After the field plate is formed, a heat treatment process is performed to change the saturated ferroelectric polarization intensity and hysteresis loop of the ferroelectric polarization film, thereby enhancing the field-effect characteristics of the device gate. Other front and back processes are the same as those for typical GaN field-effect transistor devices and are not the focus of this invention, so they will not be described further.

[0033] The embodiments described in this invention are intended to better explain a GaN field-effect transistor with a ferroelectric polarization coupling field plate and its fabrication method. The process steps of this invention are relatively simple, and the fabrication process is compatible with the technology used in the production of GaN microwave and millimeter-wave chips.

[0034] The use of ferroelectric materials as field plates, as shown in the accompanying figures, to enhance the control of the channel electric field through the induced electric field of their electric dipoles is the focus of this invention, reflecting its substantial features and advancements. The epitaxial material structure can be adjusted according to actual application needs, such as selectively introducing an AlN insertion layer 106, an AlGaN back barrier layer 105, and other device structures. The thickness of each layer, as well as the Al content and thickness of the AlGaN barrier layer, can be adjusted according to the application characteristics of the actual device. Furthermore, the types and thicknesses of the metal oxide materials, ferroelectric materials, and metal materials in the ferroelectric polarization film can be adjusted as needed. Modifications can also be made to the dielectric thickness, the material selection of the gate thickening metal system, and the material and thickness of the passivation layer, which will not be elaborated upon here.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A GaN field-effect transistor with a ferroelectric polarization coupling field plate, characterized in that, The structure includes a GaN epitaxial structure (108) and source metal (201), drain metal (205), source-drain protection dielectric (202), gate metal (203) and ferroelectric coupling field plate (204) fabricated on the GaN epitaxial structure (108); the GaN epitaxial structure (108) includes, from bottom to top: substrate (101), nucleation layer and high-resistivity buffer layer (102), channel layer (103) and barrier layer (104); the ferroelectric coupling field plate (204) is located between the gate metal (203) and the drain metal (205) and does not contact either of them.

2. A GaN field-effect transistor with a ferroelectric polarization coupling field plate according to claim 1, characterized in that, The ferroelectric polarization coupling field plate (204) includes a metal underlayer (206) and a ferroelectric material layer (207) from bottom to top. The ferroelectric material has ferroelectric polarization characteristics. The metal underlayer (206) is prepared on the source-drain protection dielectric (202). The ferroelectric polarization coupling field plate (204) is a standalone structure without power, or it is connected to the source metal (201).

3. A GaN field-effect transistor with a ferroelectric polarization coupling field plate according to claim 2, characterized in that, The metal base layer (206) contains at least one of Cr, Mu, Al, Ta, Ti, Pt, Pd, Ru, and Au; the ferroelectric material layer (207) contains at least one of perovskite ferroelectric material, lithium oxide ferroelectric material, bronze mineral ferroelectric material, bismuth layered perovskite structure ferroelectric material, two-dimensional AB type layered stacked material, and multi-domain ferroelectric material.

4. A GaN field-effect transistor with a ferroelectric polarization coupling field plate according to claim 3, characterized in that, The perovskite-type ferroelectric materials include BaTiO3, PbTiO3, PbTiZrO3, and KNbO3; the lithium oxide-type ferroelectrics include LiNbO3, LiTaO3, and BiFeO3; and the bronze-type ferroelectrics include PbTa2O6, PbNb2O6, and Ba2Sr3Nb. 10 O 30 The bismuth layered perovskite ferroelectric material includes SrBi2Ta2O9 ferroelectric material; the two-dimensional AB type layered stacked material includes BN, AlN, ZnO, MoS2, and GaSe. The multidomain ferroelectric material is Hf x Zr 1-x O2.

5. A GaN field-effect transistor with a ferroelectric polarization coupling field plate according to claim 1, characterized in that, The source / drain protection medium (202) is at least one of SiN, SiO2 medium or metal oxide MgO, Al2O3, HfO2, ZrO.

6. A GaN field-effect transistor with a ferroelectric polarization coupling field plate according to claim 1, characterized in that, The substrate (101) is any one of Si single crystal, sapphire, high-purity semi-insulating SiC, GaN single crystal, and diamond substrate.

7. A GaN field-effect transistor with a ferroelectric polarization coupling field plate according to claim 1, characterized in that, The nucleation layer and the high-resistivity buffer layer (102) are at least one of AlGaN, iron-doped GaN, vanadium-doped GaN, AlN, AlN / GaN superlattice, and AlGaN / GaN superlattice materials.

8. A GaN field-effect transistor with a ferroelectric polarization coupling field plate according to claim 1, characterized in that, The channel layer (103) is one of GaN or InGaN materials.

9. A GaN field-effect transistor with a ferroelectric polarization coupling field plate according to claim 1, characterized in that, The barrier layer (104) is any one of AlGaN, AlInN, AlN, AlInGaN, and P-type GaN.

10. A GaN field-effect transistor with a ferroelectric polarization coupling field plate according to claim 1, characterized in that, The substrate (101) has a thickness of 400 μm-1500 μm, the nucleation layer and high-resistivity buffer layer (102) has a thickness of 1500 nm, the channel layer (103) has a thickness of 200 nm, the barrier layer (104) has a thickness of 20 nm, the gate metal (203) has a thickness of 200-1000 nm, and the ferroelectric polarization coupling field plate (204) has a thickness of 70-250 nm.

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