Nitride Semiconductor Device Gate Current Suppression
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Solution Overview
Problem
Nitride semiconductor HEMTs used in power devices face challenges in being normally-off type, leading to excessive gate current due to surge voltages and parasitic inductance, and existing protection diodes have unstable characteristics.
Innovation Solution
A nitride semiconductor device is designed with a normally-off transistor and a normally-on transistor in series, where the normally-on transistor limits the gate current of the normally-off transistor, using a separation groove and insulating films to manage the drain current and suppress excessive gate current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p type GaN gate layer is laminated on an AlGaN electron supply layer to eliminate the channel and realize a normally-off type, then the device can be used as a power device, but a diode is formed with the AlGaN electron supply layer and the p type GaN gate layer which turns on under large gate voltage, resulting in excessively large current flowing between the gate and source
Solution Approach 1:
An insulating film is introduced between the AlGaN electron supply layer and the p type GaN gate layer to prevent direct contact and diode formation. This intermediary layer blocks the harmful current path while allowing the gate layer to still control the channel through electric field effects, thus resolving the contradiction between achieving normally-off operation and preventing excessive gate current.
2Object-generated harmful factors
If a MIS structure with SiN insulating layer is used as a protection diode to suppress large current, then current suppression is achieved, but the protection diode is easily influenced by variation in characteristics due to composition and stress, making it difficult to produce stable characteristics
Solution Approach 1:
The patent changes the material parameter from SiN to AlN for the insulating film. AlN has superior piezoelectric properties and higher mechanical strength, which makes it less sensitive to stress and composition variations. This parameter change (material substitution) maintains the current suppression function while significantly improving characteristic stability and reducing sensitivity to manufacturing variations.
3Power
If a normally-off transistor is used in a power device, then high withstand voltage and high temperature operation are achieved, but surge voltage generated during switching causes excessive gate current due to parasitic inductance
Solution Approach 1:
The insulating film is placed beforehand between the electron supply layer and gate layer to cushion against the harmful effects of surge voltage. This pre-established protective structure prevents the surge voltage from causing excessive current, thus cushioning the system against switching transients while maintaining the high power capability of the normally-off transistor.
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 suppresses excessive gate current flow by utilizing the saturation region of the normally-on transistor's drain current characteristics, ensuring stable operation and preventing overheating in the gate control circuit.
Implementation Method 1
Due to polarization caused by lattice mismatch of GaN with AlGaN, a two-dimensional electron gas is formed inside the electron transit layer
Implementation Method 2
a channel is eliminated by a depletion layer spreading from the p type GaN gate layer to realize a normally-off type
Implementation Method 3
a diode is formed with the AlGaN electron supply layer and the p type GaN gate layer
Data Source
AI summary
A nitride semiconductor device 1 includes a first transistor 3 which is constituted of a normally-off transistor and functions as a main transistor and a second transistor 4 which is constituted of a normally-on transistor and arranged to limit a gate current of the first transistor. The first transistor 3 includes a first electron transit layer 7A constituted of a nitride semiconductor and a first electron supply layer 8A which is formed on the first electron transit layer and constituted of a nitride semiconductor. The second transistor 4 includes a second electron transit layer 7B constituted of a nitride semiconductor and a second electron supply layer 8B which is formed on the second electron transit layer and constituted of a nitride semiconductor. A gate electrode 51 and a source electrode 44 of the second transistor 4 are electrically connected to a gate electrode 16 of the first transistor 3.