FET Sensor Gate Biasing via Charge Storage
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Solution Overview
Problem
Field effect transistor (FET)-based sensors, such as EGFETs, face sensitivity issues due to insufficient potential difference between the measurement and reference electrodes, leading to inadequate sensor response, and applying a DC voltage to overcome this can cause unwanted electrochemical reactions and corrosion if not properly insulated.
Innovation Solution
Incorporating a charge storage element, like a capacitor, connected between the measurement and gate electrodes, allowing the stored charge to bias the gate during read-out without affecting the medium, thereby enhancing sensitivity by ensuring the gate voltage exceeds the threshold voltage without direct current flow through the medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DC voltage is applied to the reference electrode to bias the gate electrode and measurement electrode, then the threshold voltage is lowered and sensor sensitivity is improved, but current flows through the medium causing unwanted electrochemical reactions and corrosion
Solution Approach 1:
The charge storage element is charged in advance during a first phase when the switch is closed, storing the necessary voltage to bias the gate electrode. This preliminary charging action allows the gate to be biased without requiring continuous current flow through the medium during the measurement phase, thus preventing electrochemical reactions and corrosion while maintaining sensor sensitivity.
2Reliability
If the measurement electrode is continuously connected to the charge storage element, then the gate voltage is maintained, but transient currents flow through the medium during read-out
Solution Approach 1:
The operation is divided into distinct phases: a first phase for charging the charge storage element when the switch is closed, and a second phase for reading out the stored charge when the switch is open. This temporal segmentation allows the gate voltage to be maintained without continuous connection to the measurement electrode, eliminating transient currents through the medium during the read-out phase while ensuring gate voltage stability.
3Productivity
If the switch is kept closed to maintain connection between measurement electrode and gate electrode, then the sensor responds continuously, but current flows through the medium causing electrochemical reactions
Solution Approach 1:
The switch operates periodically, closing during the charging phase to establish connection between the measurement electrode and gate electrode for continuous sensing response, then opening during the read-out phase to disconnect and prevent current flow through the medium. This periodic switching maintains sensor productivity while preventing electrochemical reactions during the disconnected phase.
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 increases sensor sensitivity while preventing unwanted electrochemical reactions by disconnecting the measurement electrode from the charge storage element during read-out, reducing transient currents and maintaining the medium's integrity.
Implementation Method 1
a charge storage element (60) comprising a first electrode (61) configurably connected to a node (38) between the measurement electrode (36) and the gate electrode (32) and a second electrode (63) configurably connected to a known potential source
Data Source
AI summary
The present invention relates to a sensor comprising a substrate (10) carrying a field effect transistor (30) having a gate electrode (32), the sensor further comprising a measurement electrode (36) spatially separated from the gate electrode; and a reference electrode (40), said measurement electrode being in configurable conductive contact with said gate electrode, the sensor further comprising a charge storage element (60) comprising a first electrode connected to a node (38) between the measurement electrode and the gate electrode; and a second electrode configurably connected to a known potential source (80). The present invention further relates to a method of performing a measurement with such a sensor.