SOI Transistor Matching via Local Polysilicon Heater
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Solution Overview
Problem
SOI transistors in integrated circuits face significant mismatch issues due to thermal insulation, leading to errors in comparator circuits, especially in analog-to-digital converters, where small temperature changes cause substantial variations in threshold voltage, affecting the accuracy of comparator outputs.
Innovation Solution
Incorporating a matching resistance heater coupled to each transistor in SOI integrated circuits, which allows for temperature adjustment to match the threshold voltage of transistors, thereby improving matching accuracy without increasing transistor size, using embodiments such as polysilicon resistors or p-type resistance heaters adjacent to the transistor source or drain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If SOI transistors are used with buried oxide for thermal insulation, then device integration is enabled, but transistor matching accuracy deteriorates due to temperature variations
Solution Approach 1:
The patent applies parameter changes by modifying the temperature parameter of the transistor through localized heating. By changing the temperature parameter, the threshold voltage of the transistor is adjusted to compensate for manufacturing variations and achieve better matching between transistors in the integrated circuit.
Solution Approach 2:
The patent implements local quality by applying heating specifically to individual transistors or specific regions of the circuit rather than uniformly heating the entire device. This localized thermal treatment allows selective adjustment of threshold voltages for specific transistors that require matching compensation.
2Area of moving object
If transistor size is reduced to increase integration density, then device miniaturization is achieved, but mismatch between transistors increases
Solution Approach 1:
The patent uses parameter changes (temperature adjustment) to compensate for the increased mismatch that occurs when transistors are miniaturized. By adjusting the temperature parameter locally, the threshold voltage can be tuned to achieve matching even when transistors are small and more susceptible to manufacturing variations.
3Measurement precision
If threshold voltage matching is improved through temperature adjustment, then comparator accuracy is enhanced, but device complexity increases due to additional heater elements
Solution Approach 1:
The patent applies universality by using the same polysilicon gate structure to serve dual functions: as the transistor gate for normal operation and as a heating element for threshold voltage adjustment. This eliminates the need for separate heater structures, thereby reducing device complexity while maintaining the ability to improve comparator accuracy.
4Device complexity
If polysilicon gate is used as heating element, then additional heater structure is eliminated, but threshold voltage control precision may be affected
Solution Approach 1:
The patent employs the polysilicon gate structure for dual purposes: as the control gate during normal transistor operation and as a resistive heating element for threshold voltage adjustment. This multi-functional approach simplifies the device structure by eliminating separate heater elements while maintaining adequate threshold voltage control capability through the inherent resistance of the polysilicon gate.
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 solution effectively maintains transistor matching accuracy across temperature changes, enhancing the performance of comparator circuits and reducing errors in analog-to-digital converters by allowing for periodic recalibration, thus improving the reliability of comparator outputs.
Implementation Method 1
A method for forming a matching resistance heater coupled to a transistor
Implementation Method 2
SOI transistors are especially sensitive to variation due to heating effects because the buried oxide (BOX) upon which SOI transistors are constructed is an excellent thermal insulator
Data Source
AI summary
An integrated circuit with a matched transistor pair with a matching resistance heater coupled to each transistor of the matched transistor pair. A method for forming a matching resistance heater. A method for operating an SOI integrated circuit containing a matched transistor pair with a matching resistance heater coupled to each transistor of the matched transistor pair.