GaN Auxiliary Gate Structure for High Threshold Voltage
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Solution Overview
Problem
GaN power devices face challenges in achieving a high threshold voltage, reducing gate leakage current, and expanding the gate voltage operation window while minimizing turn-on retriggering and oscillations during high dV/dt conditions, which affects their switching performance and reliability.
Innovation Solution
The integration of an auxiliary gate terminal and a pull-down network in GaN power devices, including a high-voltage active GaN device and a low-voltage auxiliary GaN device, where the high-voltage device's gate is connected to the source of the auxiliary transistor, and the auxiliary transistor's gate is connected to the drain, forming a pull-down circuit to control the gate voltage and current levels, thereby increasing the threshold voltage and reducing gate leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pGaN gate structure is used to achieve normally-off operation, then the device can be turned off reliably, but the threshold voltage becomes low (1.5-2V) causing unwanted turn-on during operation
Solution Approach 1:
The gate control is segmented into two independent gates: an internal gate connected to the 2DEG channel for primary control, and an auxiliary gate connected to the pGaN layer for threshold adjustment. This segmentation allows independent optimization of each gate's function to achieve both reliable normally-off operation and high threshold voltage.
Solution Approach 2:
The auxiliary gate acts as an intermediary between the control circuit and the internal gate. By applying a voltage to the auxiliary gate, it modulates the threshold voltage of the internal gate, thereby preventing unwanted turn-on without directly controlling the channel current.
2Reliability
If the gate voltage operation window is expanded to prevent unwanted turn-on, then device reliability improves, but the gate leakage current increases
Solution Approach 1:
Different regions of the gate structure have different doping qualities: the internal gate region has high doping to maintain low resistance and low leakage, while the auxiliary gate region has optimized doping to provide threshold control with minimal leakage. This local quality differentiation allows the device to operate with high stability without excessive gate leakage.
3Reliability
If a high threshold voltage is implemented to prevent unwanted turn-on, then device reliability improves, but the on-state resistance increases
Solution Approach 1:
The threshold voltage is made dynamic through the auxiliary gate rather than being fixed by static doping. By dynamically adjusting the auxiliary gate voltage, the threshold can be raised to prevent unwanted turn-on during operation, while the internal gate maintains optimal doping for low on-state resistance when fully turned on.
4Productivity
If fast switching capability is implemented to improve power density, then productivity improves, but oscillations occur during switching transitions
Solution Approach 1:
The auxiliary gate provides a feedback mechanism to suppress oscillations. During switching transitions, the auxiliary gate voltage can be adjusted to counteract oscillatory behavior in the internal gate, thereby maintaining fast switching speed while eliminating harmful oscillations through active feedback 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
This configuration results in a GaN transistor with a high threshold voltage, reduced gate leakage, and an expanded gate voltage operation range, preventing turn-on retriggering and oscillations, thereby enhancing switching performance and reliability for applications in low to medium voltage ranges, including power conversion and motor drives.
Implementation Method 1
an active heterojunction transistor comprising: a first III-nitride semiconductor region comprising a first heterojunction comprising an active two dimensional carrier gas
Implementation Method 2
a first heterojunction comprising an active two dimensional carrier gas
Data Source
Figure 1
Figure 2~3
Figure 4(a)~4(c)
AI summary
The disclosure relates to power semiconductor devices in GaN technology. The disclosure proposes an integrated auxiliary (double) gate terminal and a pulldown network to achieve a normally-off (E-Mode) GaN transistor with threshold voltage higher than 2V, low gate leakage current and enhanced switching performance. The high threshold voltage GaN transistor has a high-voltage active GaN device (500) and a low-voltage auxiliary GaN device (510) wherein the high-voltage GaN device has the gate connected to the source of the integrated auxiliary low-voltage GaN transistor and the drain being the external high-voltage drain terminal and the source being the external source terminal, while the low-voltage auxiliary GaN transistor has the gate (first auxiliary electrode) connected to the drain (second auxiliary electrode) functioning as an external gate terminal. A pull-down network for the switching-off of the high threshold voltage GaN transistor is formed by additional auxiliary low-voltage GaN transistors and resistive elements connected in parallel or in series with the low-voltage auxiliary GaN transistor.