This technology can be used to develop power-efficient chemical micro-sensors with high selectivity, which have a wide range of industrial, security, and military applications.
The fundamental task in chemical sensing and detection is to transduce the presence of the chemical of interest at some predetermined concentration into a useful signal. In the vast majority of cases, the ideal sensor output takes the form of an electrical signal such as a voltage or current. Previous attempts have been made at using chemiresistive polymers -- which exhibit a change in conductivity in response to chemical binding -- directly in chemical micro-sensors by directly measuring the conductivity change. However, this approach suffers from poor analyte specificity, produces weak signal, and continuously draws power. One strategy that has been attempted to mitigate the signal-to-noise ratio limitation is to coat micro-cantilevers with chemi-resistive polymers that exhibit mechanical strain in response to chemical binding and measuring the resulting deflection of the cantilever using optical, piezoelectric, or other active measurement schemes. These analog measurement modalities are susceptible to ambient interference and remain dependent on power-consuming instrumentation. This invention provides a low-power electro-mechanical chemical micro-sensor that addresses these limitations.
This invention describes a chemical micro-sensor that operates as an electro-mechanical switch. A polymer with functional groups specific to the species of interest is deposited using initiated chemical vapor deposition (iCVD) onto an approximately 100 nm-thick micro-cantilever. Selective binding of the species of interest with the polymer coating induces stresses that result in a large deflection (relative to existing cantilever-based chemical sensing methods) at the cantilever tip, on the order of 50 μm. This large deflection causes the cantilever to come into contact with a pad, completing an electrical circuit. Instead of producing a graduated response to the degree of chemical binding, this system generates a binary signal indicating the presence of the species of interest at a predetermined critical concentration. Relying on binary switching instead of analog measurements virtually eliminates power draw when the sensor is not activated and dramatically simplifies the logic circuitry required to condition and process the signal. The on/off circuitry is also more robust against ambient interference than existing analog sensors.
- Virtually zero power draw when sensor is not activated
- Binary switching eliminates need for complex signal conditioning and processing circuitry
- Large cantilever deflection reduces sensitivity to ambient interference