Polysilicon Thermal-Diffusivity Sensor Eliminates Calibration
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Solution Overview
Problem
Existing on-chip temperature sensors, such as bandgap temperature sensors, require time-consuming calibration due to manufacturing process variations and are not suitable for advanced CMOS technologies with limited voltage headroom, making them inefficient for modern processor chips with high power densities.
Innovation Solution
A thermal-diffusivity temperature sensor integrated into a semiconductor chip, utilizing an electro-thermal filter with a polysilicon heater and thermopile, and a measurement circuit that measures temperature through constant-frequency or constant-phase architectures, reducing calibration needs and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bandgap temperature sensors are used to measure on-chip temperatures, then temperature measurement capability is provided, but calibration time increases significantly due to manufacturing process variations
Solution Approach 1:
The thermal-diffusivity temperature sensor uses intrinsic material properties of polysilicon that are naturally insensitive to manufacturing process variations. The sensor self-calibrates by measuring thermal diffusivity, a fundamental property that remains consistent across different chips and wafers, eliminating the need for external calibration services and procedures.
Solution Approach 2:
The invention changes the measurement parameter from electrical characteristics (forward voltage of silicon diode) to thermal characteristics (thermal diffusivity). This parameter change exploits the fact that thermal diffusivity of polysilicon is remarkably stable across manufacturing variations, thereby eliminating calibration requirements while maintaining measurement accuracy.
2Measurement precision
If bandgap temperature sensors are implemented, then temperature sensing is achieved, but voltage headroom requirements increase to about 1.5 V
Solution Approach 1:
The invention replaces the electrical measurement mechanism (measuring forward voltage of a silicon diode) with a thermal measurement mechanism (measuring thermal diffusivity). This substitution allows operation at lower voltages since the measurement is based on thermal response rather than electrical characteristics, reducing voltage headroom requirements to compatible levels with 1.0 V core transistor voltage CMOS technologies.
Solution Approach 2:
The measurement parameter is changed from electrical voltage (forward voltage) to thermal property (thermal diffusivity). This parameter change enables the sensor to function with lower voltage headroom since thermal diffusivity measurement does not require the high voltage swings needed for electrical diode characterization.
3Reliability
If multiple on-chip temperature sensors are integrated into modern processor chips, then temperature monitoring coverage is improved, but the calibration process becomes extremely time-consuming
Solution Approach 1:
Each temperature sensor on the chip is self-calibrating through its inherent thermal-diffusivity measurement mechanism. The polysilicon-based sensor automatically references its own material properties, eliminating the need for centralized calibration procedures and enabling parallel processing of multiple sensors without sequential calibration bottlenecks.
Solution Approach 2:
The sensor design incorporates preliminary calibration-free operation by using intrinsic material properties that are naturally consistent across manufacturing variations. The thermal-diffusivity measurement approach is prepared in advance to be inherently insensitive to process variations, so no post-manufacturing calibration action is needed for any number of sensors.
4Measurement precision
If bandgap temperature sensors are used, then temperature measurement is provided, but manufacturing process variations cause device characteristics to vary considerably from chip to chip and wafer to wafer
Solution Approach 1:
The invention changes from measuring electrical parameters (forward voltage) that are highly sensitive to manufacturing variations to measuring thermal parameters (thermal diffusivity) that are inherently stable. Thermal diffusivity is a fundamental material property that remains consistent across different chips and wafers, providing manufacturing precision immunity.
Solution Approach 2:
The sensor uses the intrinsic thermal properties of polysilicon material itself as the reference standard. Since these material properties are naturally consistent across manufacturing processes, the sensor self-corrects for variations without requiring external calibration, maintaining measurement precision despite manufacturing differences.
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 allows for accurate temperature measurement without calibration, reduces power requirements, and improves manufacturing accuracy, addressing the limitations of existing bandgap temperature sensors.
Implementation Method 1
a heater; a thermopile; and a heat-transmission medium that couples the heater to the thermopile
Implementation Method 2
the thermopile comprises a sequence of alternating N+ and P+ segments of polysilicon having opposite temperature gradients
Implementation Method 3
a heat-transmission medium that couples the heater to the thermopile, wherein the heat-transmission medium comprises a polysilicon layer sandwiched between silicon dioxide layers
Data Source
AI summary
The disclosed embodiments relate to the design of a temperature sensor, which is integrated into a semiconductor chip. This temperature sensor comprises an electro-thermal filter (ETF) integrated onto the semiconductor chip, wherein the ETF comprises: a heater; a thermopile, and a heat-transmission medium that couples the heater to the thermopile, wherein the heat-transmission medium comprises a polysilicon layer sandwiched between silicon dioxide layers. It also comprises a measurement circuit that measures a transfer function through the ETF to determine a temperature reading for the temperature sensor.