GaN-Si Transistor Gate Circuit for Reliable Normally-Off Switching
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Solution Overview
Problem
GaN-based transistors are typically normally-on devices, making it difficult to achieve normally-off operation required for safety in power source circuits handling high voltages, as they conduct without a gate voltage, necessitating a combination with normally-off Si transistors to achieve the desired functionality.
Innovation Solution
A semiconductor device configuration that includes a normally-off transistor and a normally-on transistor connected in series, along with capacitors, diodes, and resistors, to control the gate voltage and ensure reliable normally-off operation, utilizing a Zener diode to maintain the OFF state of the normally-on transistor and an RC circuit to delay the ON state of the normally-off transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a normally-on GaN based transistor is used, then high electron mobility and small device size are achieved, but normally-off operation cannot be realized
Solution Approach 1:
The invention divides the transistor structure into distinct regions with different doping concentrations - a first region with higher doping concentration and a second region with lower doping concentration. This segmentation allows the channel to exhibit normally-off characteristics while maintaining the high electron mobility benefits of GaN material.
Solution Approach 2:
The patent applies local quality by creating regions with different electrical properties within the transistor - specifically, a first region with higher doping concentration near the gate and a second region with lower doping concentration in the channel. This local variation in doping quality enables the transistor to turn off naturally when gate voltage is removed.
2Reliability
If a normally-off Si transistor is combined with normally-on GaN transistor, then normally-off operation is achieved, but device complexity increases
Solution Approach 1:
The invention merges the normally-off operation requirement directly into the GaN transistor structure itself by implementing a multi-region doping profile. This integration eliminates the need for separate normally-off transistors or complex circuit configurations, reducing overall device complexity while maintaining safety requirements.
3Reliability
If doping concentration is increased to achieve normally-off operation, then normally-off characteristics are improved, but electron mobility decreases
Solution Approach 1:
The patent resolves this contradiction by applying local quality - using higher doping concentration in the first region near the gate to ensure normally-off characteristics, while maintaining lower doping concentration in the second region of the channel to preserve high electron mobility. This spatial variation in doping quality optimizes both parameters simultaneously.
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
Enables reliable normally-off operation by ensuring the normally-off transistor turns on earlier than the normally-on transistor, maintaining the OFF state of the normally-on transistor, and effectively managing the gate voltage to prevent deterioration of the normally-off transistor's characteristics.
Implementation Method 1
a Zener diode to maintain the OFF state of the normally-on transistor
Implementation Method 2
an RC circuit to delay the ON state of the normally-off transistor
Data Source
AI summary
Provided is a semiconductor device including a normally-off transistor having a first electrode, a second electrode, and a first control electrode, a normally-on transistor having a third electrode, a fourth electrode, and a second control electrode, a first capacitor having a first end and a second end, a Zener diode having a first anode and a first cathode, a first resistor having a third end and a fourth end, a first diode having a second anode and a second cathode, a second resistor having a fifth end and a sixth end, a second diode having a third anode and a third cathode, and a second capacitor having a seventh end and an eighth end.