Electrical Characterization of Interdigitated Electrodes (IDEs)

Share this post:

Interdigitated electrodes (IDEs) are widely used as pressure sensors and transducers in the medical electronics industry. They are also used in applications such as biomedical devices, automotive electronics and industrial process control systems. Due to their high sensitivity, IDEs have found use as strain gauges and force sensors in these industries. To characterize IDEs, electrical measurements need to be carried out on them since they can store charge and exhibit capacitance under certain conditions. This article discusses important characteristics of IDEs, including resistance, capacitance and impedance.

Overview of Interdigitated Electrodes

An interdigitated electrode (IDE) is a type of electrode that consists of two sets of closely-spaced fingers that are designed to make contact with the surface of a material being studied. The fingers are separated by small gaps, typically on the micrometer scale.

interdigitated electrodes on silicon wafer, electrical testing resistance, capacitance, impedance

Fingers can be made from different metals and are electrically isolated from each other electrically. IDEs have high resolution, low noise and can operate at high frequencies. They are commonly used in devices such as pressure sensors, strain sensors and RFID readers.

For example, an IDE coated with a polymer may be used as a strain gauge. When the electrodes are pulled apart, this causes the capacitance to increase, which can then be correlated to the distance between the fingers of the IDE.

Capacitance, Resistance, and Impedance

An IDE can be modeled as a circuit containing a resistor and a capacitor in series. The capacitance is a measurement of the charge stored in the system, while the resistance indicates the energy dissipated when electrical current flows through the system. Similar to the resistance, the impedance measures the opposition to alternating (e.g. sinusoidal) electrical current flows. Impedance (Z) and resistance (R) are measured in units of ohms (Ω), while capacitance (C) is typically measured in units of picoFarads (pF).

The impedance (Z) of a system at a given frequency can be measured by applying an oscillating voltage and measuring the voltage and current through the device. The relationship between these variables is known as an impedance curve. However, systems behave differently at different frequencies. For this reason, it is important to select a test frequency that is relevant to the scenario under which IDEs will be operating. In contrast, resistance and capacitance of an IDE vary little across different frequencies. For this reason, measured values of R and C can be used to characterize the performance of an IDE.

Conclusion

To summarize, this article discussed important quantities that can be used to characterize IDEs, including resistance, capacitance and impedance. Platypus Technologies fabricates custom interdigitated electrodes for your application. Typical projects include IDEs made of gold, silver or aluminum on substrates such as glass, silicon wafers, and flexible plastics. Our company also owns and operates a high-precision RLC meter that can be used to measure important electrical properties of IDEs at various frequencies.