本論文提出一種利用奈米碳管作為氣體感測元件,結合CMOS電路成為分子級感測晶片的方法,將測得之訊號直接傳入相連的CMOS訊號處理單元中,此訊號處理單元可為電流量測及阻抗量測單元,因此能夠直接量測、判斷所測得的微量電流訊號變化。後階段可於奈米碳管表面進行改質,作為生化感測元件之有效方法;並且利用陣列形式,在同時間內可偵測不同的氣體分子,以發揮氣體感測器的辨識能力,實現可穿戴式(Wearable)單晶片(SoC)的目的。 由於奈米碳管在感測氣體時,電流訊號大部分為 等級,換算成電阻單位約為Mega歐姆等級,利用訊號讀取電路做偵測,再利用公式推算出微結構的阻抗值及奈米碳管阻值。於電流訊號感測方面,本研究利用積分器將感測電流訊號轉換成電壓訊號,再藉由切換電容式電路作為訊號放大及讀出電路。本系統以TSMC 0.35 μm 2P4M製程來設計感測晶片,晶片面積為1.794*1.509μm2,工作電壓採用3.3V,以33.3kHz作為CMOS開關工作頻率、輸入100 Hz~1 kHz載波測試,可以感測範圍約1μA~數百pA之電流值。因此本研究系統確實可有效感測到微量氣體變化。
In this thesis, we disclosed a new type of gas sensor composed of CNT (carbon nanotube) and CMOS circuitry. The signal through CNT can be read directly by means of the sensing circuit. And types of the sensing circuits can be an impedance amplifier, or switched-capacitor amplifier. In the future, this sensor can detect different gas molecules after specific surface modification on CNT, and it also provides an 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. When sensing the gas, the current signal is about several nA ~ hundreds of μA. In impedance unit, it is equivalent to the level of several mega ohms. By using readout circuits, and comparing the I/O waveforms (in sine wave), we can calculate the transistor value of CNT. About measurement of current, we chose integrator converts the CNTFETs device output current into a voltage in this study. The signals are then amplified and readout with switched-capacitor (SC) circuit. We implemented the system in TSMC 0.35 μm 2P4M technology. The chip occupied 1.794*1.509μm2 with power supply voltage of 3.3V. Through simulation, the CMOS switching frequency is 30KHZ as the input signal of 1 kHz sine waves. This structure can measure the currents of about 1 micro-amp to hundreds of pico-amp. The study certainly demonstrates the sensor the small variation of gases.