Micromachined Vacuum Gauge Thermal Time-of-Flight Sensor
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Solution Overview
Problem
Current vacuum sensors face limitations in dynamic range, accuracy, and gas composition dependency, requiring multiple sensors with different principles for high vacuum applications, which complicates measurement and control processes, especially in environments with mixed gases.
Innovation Solution
A micromachined vacuum sensor employing the thermal time-of-flight sensing principle, using thermistors and a thermopile on a thermally isolated membrane, measures thermal conductivity, convection, and radiation to achieve gas-independent vacuum pressure measurement across a wide range, from ambient to ultra-high vacuum, with enhanced sensitivity and fast response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If thermal conductivity measurement is used for vacuum sensing, then measurement simplicity is improved, but measurement precision deteriorates at high vacuum due to reduced collision probability
Solution Approach 1:
The patent combines three different measurement principles (thermal conductivity, thermal convection, and thermal radiation) into a single integrated sensor system. The sensor includes a hot wire for thermal conductivity measurement, temperature sensors for detecting thermal convection effects, and the system measures thermal radiation at ultra-high vacuum. This merging allows the sensor to maintain measurement precision across the entire vacuum range from ambient to ultra-high vacuum (10^-8 Torr) without requiring multiple separate sensors.
2Measurement precision
If multiple vacuum sensors with different measurement principles are used to cover high vacuum range, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent creates a universal vacuum sensor that can measure across the entire vacuum range from ambient pressure to ultra-high vacuum (10^-8 Torr) using a single device. The sensor integrates multiple measurement capabilities (thermal conductivity, thermal convection, and thermal radiation detection) into one unified system, eliminating the need for multiple separate vacuum sensors with different measurement principles. This multi-functional design simplifies the overall system while maintaining high measurement precision across all vacuum ranges.
3Ease of manufacture
If Pirani gauge is used for low vacuum measurement, then ease of manufacture is improved, but measurement precision deteriorates at high vacuum due to reduced gas density
Solution Approach 1:
The patent implements a dynamic measurement system that automatically adapts its measurement principle based on the vacuum level. The sensor includes a hot wire for thermal conductivity measurement that operates effectively at low vacuum, while also incorporating temperature sensors and control circuitry that activate thermal convection and thermal radiation measurements at higher vacuum levels. This dynamic adaptation allows the sensor to maintain manufacturing simplicity while achieving high measurement precision across the entire vacuum range, transitioning between different measurement modes as needed.
4Measurement precision
If ion gauge is used for high vacuum measurement, then measurement precision is improved, but device complexity and cost increase due to high voltage requirements
Solution Approach 1:
The patent replaces the complex high-voltage ionization measurement system with a thermal-based measurement system. Instead of using ion gauges that require high voltage and complex electronics, the invention uses a hot wire with temperature sensors to measure thermal convection and thermal radiation effects. This substitution eliminates the need for high voltage power supplies and complex ionization circuits, significantly reducing device complexity and cost while maintaining high measurement precision in the high vacuum range (10^-8 Torr).
5Ease of operation
If thermal conductivity measurement is used, then ease of operation is improved, but measurement precision deteriorates due to gas composition dependency
Solution Approach 1:
The patent uses thermal convection and thermal radiation as intermediary measurement mechanisms to overcome gas composition dependency. The system includes temperature sensors that detect thermal convection effects caused by gas molecules interacting with the hot wire, and measures thermal radiation at ultra-high vacuum. These intermediary measurements provide information about gas density and pressure that is independent of gas composition, allowing the sensor to maintain measurement simplicity while achieving gas-independent measurement precision across different gas types and mixtures.
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 sensor provides accurate, gas-independent vacuum measurement over a large dynamic range, ensuring process stability and repeatability, with a miniature design suitable for portable applications and easy manufacturing, while eliminating the need for multiple sensors.
Implementation Method 1
utilizes the physical phenomenon that when gas molecules collide with a heated metal wire, there will be heat transfer or the thermal conductivity measured via the metal wire will change with the variations of the vacuum
Implementation Method 2
measures thermal conductivity, convection, and radiation to achieve gas-independent vacuum pressure measurement
Implementation Method 3
measures thermal conductivity, convection, and radiation to achieve gas-independent vacuum pressure measurement
Data Source
AI summary
The design of a vacuum gauge utilizing a micromachined silicon vacuum sensor to measure the extended vacuum range from ambient to ultrahigh vacuum by registering the gas thermal properties at each vacuum range is disclosed in the present invention. This single device is capable of measuring the pressure range from ambient and above to ultrahigh vacuum. This device applies to all types of vacuum measurement where no medium attack silicon is present. The disclosed vacuum gauge operates with thermistors and thermopile on a membrane of the thermal isolation diaphragm structure with a heat isolation cavity underneath.