Partial Finger Current Sensing FETs for GaN
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Solution Overview
Problem
Current sense FETs face inaccuracies in current sensing due to variations in drain-to-source resistance (RDS) as a function of temperature and applied drain-source voltage, especially in gallium nitride (GaN) FET devices, making it difficult to maintain a constant current sensing ratio over a wide range of parameters and conditions.
Innovation Solution
The implementation of multiple sense FETs and sense resistors in a high-voltage MOSFET structure, where each sense transistor has a separate source region and is coupled with a sense resistor, allowing for accurate current measurement and control by dividing the source electrode finger into sections with different lengths and resistances to handle varying current levels and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single sense FET is used to sample current, then the device complexity is low, but the measurement precision deteriorates due to RDS variations with temperature and voltage
Solution Approach 1:
The sense FET channel region is divided into multiple discrete sense FETs (first sense FET, second sense FET, etc.), each with separate source and drain regions. This segmentation allows different sense FETs to operate at different current levels and temperature conditions, thereby improving overall current sensing accuracy across varying operating conditions while managing device complexity through systematic division of the sensing function.
2Adaptability or versatility
If multiple sense FETs with different channel dimensions are used, then the adaptability to different current levels improves, but the device complexity increases
Solution Approach 1:
Multiple sense FETs with different channel dimensions are integrated into a unified current sensing system that can universally handle a wide range of current levels. Each sense FET serves multiple purposes: current sensing, temperature compensation, and adaptation to different operating conditions. The system achieves multi-functionality by selectively activating appropriate sense FETs based on the current level and temperature, thereby covering a broad current range while managing device complexity through coordinated operation of the sense FET array.
Data Source
AI summary
A lateral semiconductor field-effect transistor (FET) device fabricated on a substrate includes a high-voltage main FET having interdigitated, elongated source and drain electrode fingers each of which is electrically connected to a respective interdigitated, elongated source and drain region disposed in the substrate. The FET device further includes first and second sense FETs each having a drain region in common with the high-voltage main FET. The sense FETS also include respective first and second elongated source electrode fingers each of which is electrically connected to respective first and second elongated source regions of the first and second sense FETs, respectively. The first and second elongated source electrode fingers are disposed length-wise adjacent to one of the elongated drain electrode fingers. The first elongated source finger has a first length, and the second elongated source finger has a second length, the second length being less than the first length.