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Novel gas sensor characterization facility supports sensor development

Holst Centre has installed an experimental set-up that provides a flexible platform for gas sensor testing. This gas sensor characterization facility will support the ongoing developments of (bio)chemical sensors.

The gas sensor characterization facility consists of a gas mixing set-up, a custom-made probe station, and a semiconductor parameter analyzer. This experimental set-up was built to complement the development of gas sensors by providing a flexible platform for testing. The samples are contacted by means of adjustable probes in an enclosed, controlled environment. As a result, the devices can be monitored in the middle of the fabrication process with no need to bond them in a package. Electrical measurements can be performed while gases are flowing with varying concentrations. Therefore, transient responses and responses to increasing concentrations can be measured without opening the vessel. Several different gases can be used in the set-up because gas mixing components can be added or changed easily. A detailed description of the different elements of this gas sensor characterization facility is given below:

Gas mixing set-up

A stream of gas with a well-defined composition is generated with a gas mixing set-up. Nitrogen or dry air can be chosen as the main gas stream with an optional water bubbler for humidity control. A variable concentration of a gaseous analyte or a vapor can be obtained by injection of a trace into the main gas flow. Concentrations can be adjusted to application-relevant levels.

Probe station

The stream of gas from the gas mixing set-up is led through to a custom-made four-probe station. This includes a small chamber where the sample is located and contacted by four electrical probes that are vacuum sealed. A controlled atmosphere is thus created within the confined space of the chamber, which can contain a 150mm diameter wafer. Gas is continuously flowing through the chamber to avoid concentration changes. The chuck temperature can be controlled in a range from –200°C to +200°C. The complete probe station was manufactured by Materials Development Corporation. A magnifying stereoscope is mounted on the set-up to facilitate the placement of the probe tips on the contact pads.

Semiconductor parameter analyzer

The sensor response to the gaseous analyte is monitored by a semiconductor parameter analyzer (Agilent B1500). Four source-meter units are available so that more complex devices can be characterized. The maximum voltage and current ranges are 100V and 100mA, respectively. The minimum voltage and current resolutions are 0.5mV and 1fA, respectively. A complex-impedance measurement unit (from 1kHz to 5MHz) is also included in the system. Resistive, capacitive, and inductive measurement geometries are thus also possible. Computer-controlled hardware makes it possible to fully automate the measurement sequences. The gas sensor characterization facility was built in the frame of the activities on sensors and actuators, which focus on the development of generic sensor technologies for low-power, wireless and autonomous electronic devices. The current interest is focused on (bio)chemical sensors. Applications are found in the industrial, domestic, environmental, agricultural, logistical, and medical fields.