Bipolar Transistor Stress Sensor Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Mechanical stress exerted by packaging on semiconductor dies affects the reliability of circuitry, particularly in components like Hall sensors and temperature sensors, due to mismatched thermal expansion coefficients and chemical cure shrinkage, leading to reduced accuracy and performance.
Innovation Solution
A circuitry utilizing bipolar junction transistors to determine mechanical stress levels based on current gain, with a combination of npn and pnp transistors to enhance sensitivity and reduce temperature dependence, allowing for the measurement of stress components σxx+σyy with high sensitivity and minimal crosstalk from other stress components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical stress measurement is implemented using conventional methods, then stress detection capability is provided, but temperature dependence reduces measurement accuracy
Solution Approach 1:
The patent changes the measurement parameter from direct resistance measurement to current gain measurement. The current gain β of bipolar transistors exhibits a different temperature dependence characteristic compared to resistance, allowing stress measurement with reduced temperature influence. By measuring the ratio of collector current to base current, the system achieves stress detection that is less sensitive to temperature variations.
Solution Approach 2:
The patent employs a composite structure using both NPN and PNP bipolar transistors with opposite doping types. These transistors are designed with complementary stress sensitivity characteristics, where one type responds positively to stress while the other responds negatively. By combining their outputs, the system achieves enhanced stress measurement capability with temperature effects partially canceling out.
2Measurement precision
If single-type transistors are used for stress measurement, then circuit simplicity is maintained, but measurement sensitivity is insufficient
Solution Approach 1:
The patent combines NPN and PNP bipolar transistors in a complementary configuration. These opposite-type transistors exhibit opposite stress sensitivity, allowing their combined output to amplify the stress signal while canceling temperature effects. This composite approach achieves high measurement sensitivity without requiring excessively complex circuitry, as the complementary nature of the transistors provides inherent signal enhancement.
Solution Approach 2:
The bipolar transistors serve multiple functions simultaneously: they act as both the sensing element for stress detection and as amplification elements. The current gain measurement provides both the stress signal and the necessary signal amplification in a single component, eliminating the need for separate sensing and amplification stages.
3Reliability
If stress compensation is not implemented, then circuit simplicity is maintained, but reliability of stress-sensitive circuits deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the measured stress signal is used to compensate for stress-induced errors in other circuits. The stress measurement from the bipolar transistors provides feedback information about the mechanical stress state, which can then be used to adjust or compensate for stress effects in sensitive circuits like Hall sensors or temperature sensors, improving their reliability under stress conditions.
Solution Approach 2:
The bipolar transistors automatically sense the mechanical stress affecting the semiconductor die and generate a compensating signal. The system uses the stress-sensitive property of the transistors themselves to provide the compensation signal, eliminating the need for external compensation components or complex additional sensing mechanisms.
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 provides a high-sensitivity mechanical stress level signal with reduced temperature dependence, improving the accuracy and reliability of semiconductor die components by effectively measuring and compensating for mechanical stress, thereby enhancing the performance of stress-sensitive circuits.
Implementation Method 1
A linear relation between a stress vector T and a normal vector n follows from the fundamental laws of conservation of linear momentum and static equilibrium of forces. The components of the Cauchy stress tensor at every point in a material satisfy the equilibrium equations
Data Source
AI summary
A stress sensor includes a semiconductor die to which a mechanical stress is applied. The semiconductor die includes at least one bipolar junction transistor; at least one current source configured to inject at least one current through the at least one bipolar junction transistor; and a processing circuit configured to measure a first current gain and a second current gain of the at least one bipolar junction transistor based on the at least one injected current, to determine a first mechanical stress level based on the first current gain, to determine a second mechanical stress level based on the second current gain, and to generate a mechanical stress level signal based on the first mechanical stress level and the second mechanical stress level, wherein the mechanical stress level signal represents the applied mechanical stress, at least a portion of which is applied to the at least one bipolar junction transistor.