Nitride Semiconductor Gate Electrode Barrier Height Optimization
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Solution Overview
Problem
Nitride semiconductor HEMTs used in power devices face challenges as they are typically normally-on type, leading to high gate leakage current due to insufficient energy barriers between the gate electrode and the nitride semiconductor gate layer, which increases power consumption and heat generation.
Innovation Solution
A nitride semiconductor device configuration with a ridge-shaped gate layer containing an acceptor-type impurity and a gate electrode composed of a Ti metal film and a TiN film, where the TiN film forms on the surface of the nitride semiconductor layer, increasing the barrier height and reducing gate leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a TiN gate electrode is used to form a Schottky junction with the p-type GaN gate layer, then the device can be made normally-off type, but the energy barrier is insufficient causing large gate leakage current
Solution Approach 1:
The gate electrode is divided into multiple layers: a TiN layer in contact with the p-type GaN gate layer to provide the Schottky junction and normally-off characteristic, and an additional Ti layer on top to increase the overall barrier height. This segmentation allows each layer to fulfill specific functions that collectively solve the contradiction between achieving normally-off operation and reducing gate leakage current.
Solution Approach 2:
The gate electrode uses a composite structure of TiN and Ti materials. The TiN layer provides the necessary Schottky barrier properties for normally-off operation, while the Ti layer contributes to increasing the overall energy barrier height. This composite material approach enables the gate electrode to simultaneously achieve both normally-off characteristics and reduced gate leakage current.
2Loss of energy
If the energy barrier between gate electrode and nitride semiconductor gate layer is increased to reduce gate leakage current, then power consumption decreases, but the device complexity increases due to additional metal layers
Solution Approach 1:
The invention changes the physical parameters of the gate electrode by selecting specific materials (TiN and Ti) with appropriate barrier heights and conducting thickness optimization. By adjusting the thickness of each layer and selecting materials with specific electrical properties, the overall barrier height is increased to reduce gate leakage current while keeping the structural complexity manageable through parameter optimization rather than adding numerous layers.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The configuration effectively reduces gate leakage current by increasing the barrier height, enabling the nitride semiconductor HEMT to operate as a normally-off type device, improving efficiency and reducing heat generation in power circuits.
Implementation Method 1
a second metal film that is formed on the first metal film and is made of TiN
Implementation Method 2
the gate electrode is made of TiN (titanium nitride) that forms a Schottky junction with the p-type GaN gate layer
Implementation Method 3
Due to polarization caused by a lattice mismatch between GaN and AlGaN, a two-dimensional electron gas is formed in the electron transit layer
Implementation Method 4
polarization caused by a lattice mismatch between GaN and AlGaN
Data Source
AI summary
There is provided a nitride semiconductor device that includes a first nitride semiconductor layer configured as an electron transit layer, a second nitride semiconductor layer formed on the first nitride semiconductor layer and configured as an electron supply layer, a ridge-shaped nitride semiconductor gate layer disposed on the second nitride semiconductor layer and including an acceptor-type impurity, and a gate electrode formed on the nitride semiconductor gate layer. The gate electrode includes a first metal film that is formed on the nitride semiconductor gate layer and is mainly made of Ti, and a second metal film that is formed on the first metal film and is made of TiN.