AlGaN HEMT Gate Threshold Voltage via Piezoelectric Polarization
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Solution Overview
Problem
Existing semiconductor devices with high electron mobility transistors (HEMTs) face challenges in achieving a normally-OFF state with high gate threshold voltage while avoiding increased channel resistance and sacrificing switching characteristics due to oxidation of the electron transit layer and low carrier mobility from p-type impurities.
Innovation Solution
The semiconductor device incorporates a back barrier layer of AlXGa(1-X)N, an electron transit layer of AlaInbGa(1-a-b)N, and a top barrier layer of AlYGa(1-Y)N, with the top barrier layer preventing oxidation of the electron transit layer and creating a piezoelectric polarization to increase the gate threshold voltage, and a manufacturing method that forms these layers to suppress channel resistance and enhance carrier mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p type back barrier layer is used to increase gate threshold voltage, then the gate threshold voltage is increased, but carrier mobility is reduced due to low carrier mobility from p-type impurities
Solution Approach 1:
The patent changes the material parameters of the back barrier layer from p-type to n-type doping, fundamentally altering the carrier type and mobility characteristics. This allows achieving high gate threshold voltage through the n-type back barrier layer combined with the double heterostructure, without the carrier mobility penalty associated with p-type impurities.
2Ease of operation
If the electron transit layer is exposed to achieve normally-OFF operation, then normally-OFF operation is achieved, but channel resistance increases due to oxidation of the electron transit layer
Solution Approach 1:
The patent applies preliminary protective action by forming the n-type back barrier layer and top barrier layer to create a protective structure that prevents oxidation of the electron transit layer before exposure issues can occur. The n-type back barrier layer serves as a protective barrier that prevents oxygen diffusion to the electron transit layer, thereby maintaining low channel resistance while enabling normally-OFF operation.
Solution Approach 2:
The n-type back barrier layer acts as an intermediary protective layer between the electron transit layer and the ambient environment. This intermediate layer prevents direct oxidation of the electron transit layer while still allowing the device to achieve normally-OFF operation through the engineered heterostructure.
3Reliability
If a double heterostructure with n-type back barrier layer is used, then gate threshold voltage is increased and channel resistance is suppressed, but device complexity increases
Solution Approach 1:
The n-type back barrier layer serves multiple functions simultaneously: it increases the gate threshold voltage through the double heterostructure effect, suppresses channel resistance by preventing oxidation of the electron transit layer, and provides structural support. This multi-functionality reduces the need for additional separate layers or structures, thereby limiting the increase in device complexity.
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 solution effectively increases the gate threshold voltage, suppresses channel resistance, and improves carrier mobility, enabling reliable normally-OFF operation while maintaining high electron mobility.
Implementation Method 1
the top barrier layer preventing oxidation of the electron transit layer and creating a piezoelectric polarization to increase the gate threshold voltage
Data Source
AI summary
A semiconductor device includes: a back barrier layer containing AlXGa(1-X)N (0<X≤1); an electron transit layer containing AlaInbGa(1-a-b)N (0≤a+b≤1) and formed on the back barrier layer; a top barrier layer containing AlYGa(1-Y)N (0<Y≤1) and formed on the electron transit layer; an electron supply layer containing AlZGa(1-Z)N (0<Z≤1) and formed on the top barrier layer, the electron supply layer having an opening to expose the top barrier layer; a two-dimensional electron gas region formed in an area of a surface layer portion of the electron transit layer, the area opposing the electron supply layer with the top barrier layer interposed between the electron supply layer and the area; a gate insulating layer formed in the opening of the electron supply layer; and a gate electrode layer formed on the gate insulating layer and opposing the electron transit layer with the gate insulating layer interposed therebetween.