pH Sensor Floating Gate Transistor Temperature Compensation
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Solution Overview
Problem
Existing pH sensors that use electrolyte-insulator-semiconductor field-effect transistors (ISFETs) with reference electrodes, such as silver/silver chloride, are costly and complex to manufacture, and simpler alternatives like platinum or gold electrodes experience erratic voltage drift over time.
Innovation Solution
A pH sensor design that includes a semiconductor die with a metallization structure, dielectric layer, and electrodes, where the temperature of the fluid is controlled to measure pH using a heating apparatus and floating gate transistor, eliminating the need for an external reference electrode by measuring voltage at different temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simplified reference electrode (Pt, Au, IrOx, RuO2) is used instead of Ag/AgCl, then manufacturing cost and complexity are reduced, but voltage drift becomes erratic over time
Solution Approach 1:
The patent introduces a floating gate capacitor as an intermediary element between the simplified reference electrode and the measurement circuit. This capacitor couples the electrode to the transistor gate, allowing the system to achieve stable pH measurements without requiring a complex Ag/AgCl reference electrode, thus resolving the contradiction between simplicity and reliability
Solution Approach 2:
The patent changes the operating parameters by measuring voltage at different temperatures (temperature compensation). By controlling and measuring temperature, the system compensates for voltage drift in simplified reference electrodes, maintaining measurement reliability while using cost-effective electrode materials
2Reliability
If temperature control is implemented to compensate for voltage drift, then measurement stability is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent merges the temperature control function with the existing pH sensing structure by integrating a heater directly on the semiconductor die. This consolidation achieves temperature compensation without adding separate external temperature control equipment, resolving the contradiction between measurement stability and device complexity
Solution Approach 2:
The integrated heater enables the sensor to self-regulate its operating temperature, compensating for voltage drift autonomously. This self-service approach improves measurement stability without requiring complex external temperature control systems
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 reduces manufacturing costs and complexity while providing stable pH measurements by controlling fluid temperature to compensate for voltage drift, offering a cost-effective and reliable pH sensing solution without an external reference.
Implementation Method 1
the heater circuit is configured to deliver a current signal to the metal resistor to selectively heat the fluid
Implementation Method 2
The third electrode is coupled to the transistor gate and is separated by the dielectric layer from the sensing side to form a capacitor between the fluid and the gate
Implementation Method 3
The gate is coupled to the third electrode to sense a potential of the fluid through a capacitor formed by the dielectric layer between the fluid and the third electrode
Data Source
AI summary
For sensing pH of a fluid, a heating apparatus of a semiconductor die controls a temperature of the fluid to a first temperature. A first voltage of a gate of a floating gate transistor of the semiconductor die is measured while the temperature of the fluid is at the first temperature. Also, the heating apparatus controls the temperature of the fluid to a second temperature that is different than the first temperature. A second voltage of the gate is measured while the temperature of the fluid is at the second temperature. The pH of the fluid is determined based on the first and second voltages, the first temperature and the second temperature.