Nitride Semiconductor Gate Insulation for Leakage Control
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Solution Overview
Problem
Nitride semiconductor devices with Schottky junctions experience high gate leak current and threshold voltage fluctuations due to the interface traps formed between the nitride semiconductor gate layer and the gate electrode, limiting their application as normally-off power devices.
Innovation Solution
A nitride semiconductor device is designed with a gate insulating film interposed between the nitride semiconductor gate layer and the gate electrode, using SiN or SiO2 films, which reduces gate leak current and suppresses threshold voltage fluctuations by pinning the barrier height, thereby enabling a normally-off operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gate electrode is formed in Schottky junction with the p type GaN gate layer, then electrical connection is achieved, but gate leak current becomes large and the gate layer degrades readily
Solution Approach 1:
An insulating film is introduced as an intermediary layer between the metal gate electrode and the p-type GaN gate layer. This intermediary prevents direct Schottky junction formation, thereby reducing gate leak current and preventing gate layer degradation while maintaining electrical functionality through capacitive coupling.
Solution Approach 2:
The insulating film acts as a protective sacrificial layer that prevents degradation of the expensive and critical p-type GaN gate layer. By allowing the insulating film to bear the stress and potential damage, the valuable semiconductor gate layer is preserved from degradation.
2Object-generated harmful factors
If a gate insulating film is formed on the nitride semiconductor gate layer, then gate leak current is reduced, but interface traps are formed causing threshold voltage fluctuation
Solution Approach 1:
A composite gate structure is formed by combining the metal gate electrode with the insulating film and the p-type GaN gate layer. This composite structure leverages the low leakage properties of the insulator while using the metal for electrical connectivity, and the doped GaN layer to compensate for threshold voltage shifts through carrier accumulation.
Solution Approach 2:
The insulating film thickness is optimized to balance leakage reduction with electric field control. By carefully controlling the thickness parameter, the film provides sufficient insulation to reduce leak current while maintaining appropriate electric field distribution to minimize threshold voltage instability.
3Ease of operation
If a p type GaN gate layer is used to eliminate the channel, then normally-off operation is achieved, but Schottky junction with metal gate causes degradation
Solution Approach 1:
The insulating film serves as a protective intermediary between the metal gate electrode and the p-type GaN gate layer, preventing direct chemical and electrical interaction that causes degradation. This allows the p-type gate layer to fulfill its normally-off function without suffering from Schottky junction-related degradation.
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 reduces gate leak current to less than 1 nA/mm and stabilizes the threshold voltage, making the device suitable for power applications by preventing degradation and ensuring reliable operation.
Implementation Method 1
a gate insulating film, formed on the gate metal film
Implementation Method 2
suppresses threshold voltage fluctuations by pinning the barrier height
Data Source
AI summary
A nitride semiconductor device 1 includes a first nitride semiconductor layer 4, constituting an electron transit layer, a second nitride semiconductor layer 5, formed on the first nitride semiconductor layer 4 and constituting an electron supply layer, a nitride semiconductor gate layer 6, disposed on the second nitride semiconductor layer 5 and containing an acceptor type impurity, a metal film 7, formed on the nitride semiconductor gate layer 6, and a gate pad 23, connected to the metal film 7 via a gate insulating film 8 having a first surface and a second surface, the first surface of the gate insulating film 8 is electrically connected directly or via a metal to the metal film 7, and the second surface of the gate insulating film 8 is electrically connected directly or via a metal to the gate pad 23.