Ferroelectric Gate HEMT Structure for Normally-Off Operation
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Solution Overview
Problem
High-Electron-Mobility-Transistors (HEMTs) based on III-N structures are typically normally-on due to a permanent 2DEG, making them unsafe and difficult to integrate into logic gates, and existing solutions for normally-off structures suffer from low threshold voltages and high gate leakage currents.
Innovation Solution
Incorporating a ferroelectric third layer made of a nitride compound or oxide compound with zinc, which allows for a high threshold voltage by shifting the polarization direction, enabling a normally-off state with minimal leakage current, and maintaining stability even at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a p-doped AlGaN gate is used to achieve higher threshold voltages, then the threshold voltage is improved, but high gate leakage currents arise due to Schottky or ohmic contact effects
Solution Approach 1:
A ferroelectric layer is introduced as an intermediary between the gate electrode and the AlGaN gate. This ferroelectric layer mediates the electrical field distribution, enabling high threshold voltage control without direct Schottky contact between the gate metal and the semiconductor, thereby eliminating gate leakage currents while maintaining effective gate control.
Solution Approach 2:
The invention changes the electrical parameters of the gate structure by introducing a ferroelectric material with switchable polarization. By controlling the polarization state of the ferroelectric layer, the threshold voltage can be dynamically adjusted to high positive values, and the gate leakage is eliminated by changing the contact physics from Schottky to a ferroelectric-mediated interface.
2Area of moving object
If oxide-based ferroelectric materials are used in the gate stack, then the threshold voltage can be shifted above 0 V achieving normally-off state, but the production temperature requirements increase
Solution Approach 1:
The invention changes the material parameter of the ferroelectric layer from oxide-based to nitride-based ferroelectric materials. Nitride ferroelectrics have higher thermal stability and can be processed at lower temperatures compared to oxide ferroelectrics, thereby achieving the normally-off state with reduced production temperature requirements while maintaining high threshold voltage control.
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 use of ferroelectric nitride or oxide compounds with zinc achieves a stable and high threshold voltage, ensuring the HEMT is securely in a non-conductive state without external gate voltage, suitable for power electronics with improved long-term stability and reduced production temperature requirements.
Implementation Method 1
Incorporating a ferroelectric third layer made of a nitride compound or oxide compound with zinc, which allows for a high threshold voltage by shifting the polarization direction
Data Source
AI summary
A transistor having high electron mobility (HEMT) having a first layer and a second layer is described. The first layer has a first material made of a first nitride compound. The first nitride compound has a group III element. The second layer has a second material made of a second nitride compound. The second nitride compound has a group III element. A main surface of the second layer is arranged opposite a main surface of the first layer, such that a charge zone forms along the main surface of the second layer. The HEMT further has a gate electrode, which is arranged opposite the second layer, at least in regions, such that the second layer is arranged between the first layer and the gate electrode. Furthermore, the HEMT has a third layer, which is arranged between the gate electrode and the second layer. The third layer has a ferroelectric third material made of a third nitride compound, or a ferroelectric third material made of an oxide compound which contains zinc.