TWI869004B - Improved Field Plate Structure of GaN High Electron Mobility Transistor - Google Patents

Abstract

The present invention provides a field plate improvement structure for a gallium nitride high electron mobility transistor, which includes: an epitaxial structure, a source, a gate, a drain, a double passivation layer, and a vertical field plate; the vertical field plate structure can redistribute the electric field between the gate and the drain, which can effectively increase the breakdown voltage of the device and improve the current collapse effect.

Description

Improved field plate structure of gallium nitride high electron mobility transistor

The present invention relates to a semiconductor device structure, in particular to an improved field plate structure of a gallium nitride high electron mobility transistor.

In order to meet the market demand for high-power and high-frequency components in recent years, AlGaN/GaN high electron mobility transistors have received great attention due to their characteristics such as wide energy band and high electron saturation rate. In addition, in order to improve the breakdown voltage of components, field plate technology is widely used in components. Field plate technology can make the lateral spatial charge distribution of components more uniform, thereby increasing the breakdown voltage of components and improving the effect of current collapse. Several different field plate structures have been proposed in the prior art, such as gate field plates, source connection field plates, etc.

Although the field plate structure proposed by the prior art can increase the breakdown voltage of the device and improve the current collapse effect, these lateral or gate-connected field plate configurations will lead to an increase in Miller capacitance, which will reduce the high-frequency characteristics of the device. In addition, the gate lateral field plate will cause the distance between the gate and the drain to shorten, that is, the electron drift region to shorten, which will cause the electric field to concentrate on the gate or drain edge, causing the device breakdown voltage to decrease, so the lateral field plate structure will also limit the development of device miniaturization. Finally, field plates are mostly made of silicon nitride as the dielectric material, but its dielectric constant is lower than other high-k materials, which may reduce the effect of field plates on improving device breakdown voltage.

In summary, for high-power gallium nitride components, reliability and breakdown voltage are important indicators. In order to improve the stability of the component, we must increase the breakdown voltage of the component. The most commonly used method is to use a field plate structure. This structure can redistribute the electric field between the gate and the drain, causing the peak electric field near the gate to drop, thereby reducing the probability of hot electrons being captured by the dielectric layer, which can effectively improve the current collapse effect and increase the breakdown voltage of the component. However, due to the limitations of the traditional lateral structure on component miniaturization, the present invention will manufacture a vertical field plate structure to increase the breakdown voltage and improve the current collapse effect while miniaturizing the component.

In view of the above shortcomings of the known technology, the main purpose of the present invention is to propose an improved field plate structure of a gallium nitride high electron mobility transistor, so as to increase the breakdown voltage and improve the current collapse effect while miniaturizing the device.

To achieve the above-mentioned purpose, the present invention proposes an improved field plate structure for a gallium nitride high electron mobility transistor, which includes: an epitaxial structure; a three-electrode structure including a source, a gate and a drain disposed on the epitaxial structure, wherein the epitaxial structure forms a vertical notch at the corresponding drain; a double-layer passivation layer including an L-shaped low-k passivation layer and an L-shaped high-k passivation layer disposed in the vertical notch, and a vertical field plate disposed in the vertical direction on the double-layer passivation layer.

Preferably, the epitaxial structure from bottom to top can be: silicon carbide or silicon substrate, gallium nitride buffer layer, gallium nitride channel layer and aluminum gallium nitride barrier layer.

Preferably, the three electrodes can be set on the aluminum gallium nitride barrier layer, the source material is titanium and gold, the gate material is nickel and gold, and the drain material is titanium and gold.

Preferably, the low dielectric constant passivation layer material can be silicon nitride, silicon oxide or aluminum oxide material.

Preferably, the high dielectric constant passivation layer material can be einsteinium dioxide, yttrium oxide, titanium oxide, titanium oxide or zirconium oxide material.

Preferably, the high dielectric constant passivation layer can be disposed on the low dielectric constant passivation layer, and the vertical field plate can be disposed on the high dielectric constant passivation layer.

Preferably, the depth of the vertical notch extending into the GaN buffer layer can be greater than 1/2 of the thickness of the GaN buffer layer.

Preferably, the depth of the vertical field plate extending into the GaN buffer layer can be less than 1/2 of the thickness of the GaN buffer layer.

Preferably, it may further include a parallel field plate disposed above the double passivation layer extending from the drain to the gate.

The above overview and the following detailed description and attached figures are all for the purpose of further explaining the methods, means and effects adopted by the present invention to achieve the intended purpose. Other purposes and advantages of the present invention will be elaborated in the subsequent description and drawings.

1: Epitaxial structure

11: Gallium nitride buffer layer

12: Gallium nitride channel layer

13: Aluminum-gallium nitride barrier layer

2: Double passivation layer

21: Low dielectric constant passivation layer

22: High dielectric constant passivation layer

3: Vertical field plate

S: Source

G: Gate

D: Drain

Figure 1 is a schematic diagram of the improved field plate structure of the gallium nitride high electron mobility transistor proposed in the present invention.

Figure 2 is a data comparison of various field plate structures.

Figure 3 shows the electric field distribution of the device with parallel field plates and perpendicular field plates.

Although the present invention can be embodied in different forms, the embodiments shown in the attached drawings and described below are preferred embodiments of the present invention. Please understand that what is disclosed herein is considered as an example of the present invention and is not intended to limit the present invention to the specific embodiments shown and/or described.

Please refer to FIG. 1, which is a schematic diagram of the field plate improvement structure of the gallium nitride high electron mobility transistor proposed in the present invention, which shows a field plate improvement structure of the gallium nitride high electron mobility transistor of the present invention, which includes: an epitaxial structure 1, a three-electrode, a double-layer passivation layer 2 and a vertical field plate 3. The epitaxial structure 1 can be from bottom to top: a silicon carbide or silicon substrate, a gallium nitride buffer layer 11, a gallium nitride channel layer 12 and an aluminum gallium nitride barrier layer 13, and a gallium nitride cap layer can be further provided on the aluminum gallium nitride barrier layer 13. The three electrodes including the source S, the gate G and the drain D are arranged on the epitaxial structure 1, wherein the epitaxial structure 1 forms a vertical notch at the position corresponding to the drain D. The depth of the vertical notch extending from the drain D to the gallium nitride buffer layer 11 may be greater than 1/2 of the thickness of the gallium nitride buffer layer 11. In the present embodiment, the thickness of the gallium nitride buffer layer 11 is between 1μm-3μm, and the thickness of the gallium nitride buffer layer 11 at the position corresponding to the notch is between 0.3μm-1.4μm.

The double-layer passivation layer 2 includes an L-shaped low-k passivation layer 21 and an L-shaped high-k passivation layer 22, which are arranged in a vertical notch, and a vertical field plate 3, which is arranged on the double-layer passivation layer 2 in a vertical direction. In this embodiment, the low-k passivation layer 21 material can be silicon nitride, silicon oxide or aluminum oxide material, and the high-k passivation layer 22 material can be einsteinium dioxide, yttrium oxide, titanium oxide, titanium oxide or zirconium oxide material. The high-k passivation layer 22 is arranged on the low-k passivation layer 21, and the vertical field plate 3 is arranged on the high-k passivation layer 22.

As described above, the field plate structure is vertically extended to the gallium nitride buffer layer 11 of the epitaxial structure 1. When a positive bias is applied to the drain D, it can disperse the electric field to the gallium nitride buffer layer 11 instead of concentrating it between the gate G and the drain D, which is beneficial to improve the breakdown voltage while miniaturizing the device. In addition, a layer of high dielectric constant material (HfO ₂ ) is added to the traditional single-layer passivation layer of silicon nitride (SiN) structure to increase its breakdown voltage and improve the current collapse effect.

In addition, in this embodiment, the three electrodes are arranged on the aluminum-gallium nitride barrier layer 13, the source S is made of titanium and gold, the gate G is made of nickel and gold, and the drain D is made of titanium and gold.

In this embodiment, the depth of the vertical field plate 3 extending into the gallium nitride buffer layer 11 is less than 1/2 of the thickness of the gallium nitride buffer layer 11. For example, the thickness of the gallium nitride buffer layer 11 is between 1μm-3μm, and the depth of the vertical field plate 3 extending into the gallium nitride buffer layer 11 is between 0.2μm-1.4μm, so that the electric field between the gate G and the drain D is redistributed, which can effectively increase the breakdown voltage of the device and improve the current collapse effect.

Furthermore, the present invention can further set a parallel field plate at the drain D above the double-layer passivation layer 2. The parallel field plate extends from the drain D to the gate G to form a double field plate and double-layer passivation layer 2 structure.

Please refer to Figure 2 and Figure 3. Figure 2 is a comparison of various field plate structure data. Figure 3 is a device electric field distribution diagram of parallel field plate and vertical field plate 3. From the literature data Figure 2, it can be seen that when the distance between the device drain D and the gate G is reduced, the vertical field plate structure can help the device to better increase the breakdown voltage. The reason can be seen from the device electric field distribution diagram in Figure 3. When the spacing is reduced, the lateral field plate structure will concentrate the electric field between the gate G and the drain D. This electric field will cause hot electrons to be generated, causing the device to collapse; on the other hand, the vertical field plate 3 structure can disperse the electric field between the gate G and the drain D and the epitaxial buffer layer at the same time, which can better prevent device collapse.

In summary, due to the rapid development of high technology in recent years, the specifications and demands in the fields of high-frequency communications and high-power components have been greatly improved. Compared with other semiconductor materials, gallium nitride is regarded as the next generation to replace gallium arsenide (GaAs) because of its material properties such as bandwidth and high electron saturation rate. However, for gallium nitride transistors used in high-power components, the breakdown voltage must be an important indicator. At the same time, current collapse is also a problem that must be overcome. Current collapse will affect the performance and reliability of the component. The present invention utilizes a vertical field plate 3 structure of a double passivation layer 2 (dielectric layer) (SiN/HfO ₂ ). For high power device applications, it can not only reduce the peak electric field near the gate G, but also reduce the probability of hot electrons being captured by the dielectric layer, thereby increasing device reliability.

The above embodiments are only for illustrative purposes to illustrate the features and effects of the present invention, and are not intended to limit the scope of the substantial technical content of the present invention. Anyone familiar with this art may modify and change the above embodiments without violating the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be as listed in the scope of the patent application described below.

1: Epitaxial structure

11: Gallium nitride buffer layer

12: Gallium nitride channel layer

13: Aluminum-gallium nitride barrier layer

2: Double passivation layer

21: Low dielectric constant passivation layer

22: High dielectric constant passivation layer

3: Vertical field plate

S: Source

G: Gate

D: Drain

Claims (9)

An improved field plate structure of a gallium nitride high electron mobility transistor includes: an epitaxial structure; three electrodes, including a source, a gate and a drain, disposed on the epitaxial structure, wherein the epitaxial structure forms a vertical notch corresponding to the drain; a double-layer passivation layer, including an L-shaped low-k passivation layer and an L-shaped high-k passivation layer, disposed in the vertical notch, and a vertical field plate, disposed in a vertical direction on the double-layer passivation layer. As described in Item 1 of the patent application, the field plate improvement structure of the gallium nitride high electron mobility transistor, wherein the epitaxial structure from bottom to top is: a silicon carbide or silicon substrate, a gallium nitride buffer layer, a gallium nitride channel layer and an aluminum gallium nitride barrier layer. As described in Item 2 of the patent application, the field plate improvement structure of the gallium nitride high electron mobility transistor, wherein the three electrodes are arranged on the aluminum gallium nitride barrier layer, the source electrode is made of titanium and gold, the gate electrode is made of nickel and gold, and the drain electrode is made of titanium and gold. As described in Item 1 of the patent application scope, the field plate improvement structure of the gallium nitride high electron mobility transistor, wherein the low dielectric constant passivation layer material is silicon nitride, silicon oxide or aluminum oxide material. The field plate improvement structure of the gallium nitride high electron mobility transistor as described in Item 1 of the patent application scope, wherein the high dielectric constant passivation layer material is einsteinium dioxide, yttrium oxide, rhenium oxide, titanium oxide or zirconium oxide material. As described in Item 2 of the patent application scope, the field plate improvement structure of the gallium nitride high electron mobility transistor, wherein the high dielectric constant passivation layer is disposed on the low dielectric constant passivation layer, and the vertical field plate is disposed on the high dielectric constant passivation layer. As described in Item 6 of the patent application, the field plate improvement structure of the gallium nitride high electron mobility transistor, wherein the vertical notch extends into the gallium nitride buffer layer to a depth greater than 1/2 of the thickness of the gallium nitride buffer layer. An improved field plate structure for a gallium nitride high electron mobility transistor as described in Item 7 of the patent application, wherein the depth of the vertical field plate extending into the gallium nitride buffer layer is less than 1/2 of the thickness of the gallium nitride buffer layer. The improved field plate structure of the gallium nitride high electron mobility transistor as described in Item 2 of the patent application further includes a parallel field plate disposed above the double passivation layer extending from the drain to the gate.