Multi-Vt Transistor Circuits for Over-Drive and Noise Immunity
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Solution Overview
Problem
Existing semiconductor wafers with transistors of identical structure face challenges in achieving sufficient over-drive voltage for pull-up devices, leading to compromised noise immunity and increased static current.
Innovation Solution
The implementation of transistors with different threshold voltages (Vt) on the same semiconductor wafer, achieved through variations in gate materials, p-type doping materials, active layer thickness, material compositions, and structures, allows for the adjustment of work function differences and polarization amounts to create multiple-Vt transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the threshold voltage Vt of pull-up E-HEMT transistors is reduced to provide enough over-drive voltage and reduce static current, then the over-drive voltage is improved and static current is reduced, but the noise immunity is compromised
Solution Approach 1:
The patent applies local quality by creating different threshold voltages for different transistors on the same wafer. Specifically, transistors in the pull-up network have reduced threshold voltages to minimize static current and provide over-drive voltage, while the power switch HEMT maintains a higher threshold voltage for noise immunity. This is achieved through selective doping, varying active layer thicknesses, or using different material compositions in different regions of the wafer.
Solution Approach 2:
The patent segments the transistor population into different groups with different threshold voltage characteristics. The pull-up E-HEMT transistors are segmented to have low Vt for energy efficiency, while the power switch HEMT is segmented to have high Vt for reliability. This segmentation allows each transistor group to be optimized for its specific function without compromising the other.
2Power
If the threshold voltage Vt of all transistors on the wafer is reduced to provide over-drive voltage, then the over-drive voltage is improved, but the power switch HEMT cannot withstand large back-feed-through impulse voltage to its gate
Solution Approach 1:
The patent implements local quality by assigning different threshold voltage characteristics to different transistor locations and functions. The power switch HEMT is specifically designed with a higher threshold voltage to withstand back-feed-through impulse voltages, while other transistors in the driver stages have lower threshold voltages to provide sufficient over-drive voltage for fast switching.
Solution Approach 2:
The patent introduces intermediate transistor stages with specific threshold voltage characteristics that act as mediators between the control signal and the power switch. These intermediate transistors can have optimized threshold voltages that balance the need for over-drive voltage while protecting the power switch from direct exposure to high impulse voltages.
Data Source
AI summary
Apparatus and circuits including transistors with different threshold voltages and methods of fabricating the same are disclosed. In one example, a semiconductor structure is disclosed. The semiconductor structure includes: a substrate; an active layer that is formed over the substrate and comprises a plurality of active portions; a polarization modulation layer comprising a plurality of polarization modulation portions each of which is disposed on a corresponding one of the plurality of active portions; and a plurality of transistors each of which comprises a source region, a drain region, and a gate structure formed on a corresponding one of the plurality of polarization modulation portions. The transistors have at least three different threshold voltages.