Reference MOSFET Local Surface Temperature Measurement
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Solution Overview
Problem
Existing methods for accurately measuring local temperature of semiconductor devices under stress are inaccurate due to temperature gradients and calibration difficulties, often requiring sophisticated algorithms and potentially damaging the device.
Innovation Solution
A method using an unstressed reference MOSFET adjacent to the semiconductor device under stress, measuring drain current changes to calculate local surface temperature, with heaters minimizing temperature gradients and keeping the reference MOSFET unstressed to prevent bias-induced degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a metal line is formed at a higher level than the gate to measure temperature, then temperature sensing is achieved, but measurement precision deteriorates due to temperature gradients between different levels
Solution Approach 1:
The patent transitions from vertical temperature sensing (metal line at higher level) to surface-level temperature sensing by placing the reference MOSFET adjacent to the device under stress on the same substrate surface, eliminating temperature gradient errors caused by vertical separation
Solution Approach 2:
The patent introduces a reference MOSFET as an intermediary device that indirectly measures the temperature at the interface of interest without directly contacting it, using drain current as a temperature indicator while remaining thermally coupled to the same substrate surface
2Measurement precision
If diodes and transistors are used for temperature sensing, then temperature measurement is achieved, but device complexity increases due to sophisticated algorithms and corrections needed
Solution Approach 1:
The patent uses a reference MOSFET that is identical in structure to the device under stress but operates under normal conditions, creating a simplified copy that provides temperature information through direct comparison rather than complex calculations
Solution Approach 2:
The patent changes the operating parameter of the reference MOSFET from stressed to unstressed conditions, allowing temperature extraction through simple drain current ratio comparison without needing sophisticated algorithms or correction factors
3Measurement precision
If multiple pads are used for MOS gates to sense temperature closer to the interface, then measurement precision improves, but reliability deteriorates due to charge collection and potential device damage
Solution Approach 1:
The patent extracts the temperature sensing function from the gate structure itself (which would require multiple pads and risk charge collection) by using a separate reference MOSFET dedicated solely to temperature measurement, eliminating the reliability risk while maintaining measurement precision
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 approach provides accurate and cost-effective local temperature measurement proximate to the semiconductor device's interface, minimizing calibration adjustments and avoiding damage from stress-induced current changes.
Implementation Method 1
measuring drain current changes to calculate local surface temperature
Implementation Method 2
heaters minimizing temperature gradients
Data Source
AI summary
An apparatus and method is described for measuring a local surface temperature of a semiconductor device under stress. The apparatus includes a substrate, and a reference MOSFET. The reference MOSFET may be disposed closely adjacent to the semiconductor device under stress. A local surface temperature of the semiconductor device under stress may be measured using the reference MOSFET, which is not under stress. The local surface temperature of the semiconductor device under stress may be determined as a function of drain current values of the reference MOSFET measured before applying stress to the semiconductor device and while the semiconductor device is under stress.