| Summary: | 碩士 === 國立臺北科技大學 === 機電整合研究所 === 95 === In this thesis, we disclosed a new type of gas sensor composed of CNT (carbon nanotube) and CMOS circuitry (switched-capacitor amplifier). The signal through CNT can be read directly by means of the sensing circuit. And types of the sensing circuits can be a current amplifier, or a trans-impedance amplifier (TIA).
This sensing circuit must possess such properties as high resolution and low-signal readout ability, to show the high sensitivity of CNT-based sensor. As far as CNT-based gas sensor is concerned, the current signal is about several nA ~ hundreds of μA. Therefore, the amplifying circuit aims to detect a current signal of several nA, and to distinguish the changing value directly.
Considering of the restriction of the commonly-used trans-impedance amplifiers, we use switched-capacitor amplifier as the signal-readout circuit. The circuit is composed of two stages. The first stage is a switched-capacitor integrator, to convert current signals into voltage signals. And the second stage is the switched-capacitor amplifier, to make this signal become an easy-to-read value. Moreover, to prevent switched-capacitor amplifier from being affected by the imperfectness of OPAs, we use the technique of correlated-double sampling, CDS, to overcome this problem.
In the future, this CNT-based sensor can detect different gas molecules after specific surface modification on CNT, and it also provides a effective way in applying bio-sensors. Furthermore, an array-typed CNT-based sensor can detect various gas molecules at the same time, and it is desired to become a wearable device in the future.
This study is based on TSMC 0.35μm 2P4M process provided through CIC.
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