低雜訊讀取電路應用於 奈米碳管感測元件之研究

A Study of low noise readout circuit on carbon nanotube sensing device

葉智源(Chih-Yuan Yeh)

指導教授 ： 黃榮堂 ； 施勝雄

國立臺北科技大學/機電學院/機電整合研究所/碩士(2010年)

摘要

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。經由全差分設計的結構，提供了一個良好的雜訊抑制能力。放大器偏移電壓可以經由相關雙取樣技術給消除掉。本系統以TSMC 0.35 μm 2P4M製程來設計感測晶片，晶片面積為1.79672*2.01684 ,工作電壓採用3.3V，以25kHz作為CMOS開關工作頻率、輸入1 kHz載波測試，可以感測範圍約10nA~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。

關鍵字

奈米碳管 ； 氣體感測器 ； CMOS ； 切換電容式電路 ； 積分器

並列摘要

In this thesis, a new type of gas sensor composed of CNT (carbon nanotube) and CMOS circuitry is proposed. The gas molecules through CNT can be measured directly by means of the sensing circuit, which is composed of an impedance amplifier or a switched-capacitor amplifier. The goal of this sensor is to detect various gas molecules after modifying the specific surface of CNT. It also provides an effective way in applications of bio-sensors. Furthermore, an array-typed CNT-based sensor can be to detect various gas molecules at the same time, and it is desired to become a wearable device.
The sensing current of gas is about several nA ~ hundreds of μA. , which 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. As to measurement of current, we chose an integrator to convert the CNTFETs device output current into a voltage in this study. The sensing signals are then amplified and readout with switched-capacitor (SC) circuit. The proposed system is implemented in TSMC 0.35 μm 2P4M technology. The chip area is roughly 1.794 1.509 with power supply of 3.3V. Through simulation, the CMOS switching frequency is 25KHZ as the input signal of 1 kHz sine waves. The proposed structure has a current measuring range from 10 nano-amp to hundreds of pico-amp. This study successfully presents a smart sensor which can detect a very small concentration of gas.

並列關鍵字

Carbon Nanotubes (CNTs)Gas Sensor ； CMOS ； Switched-Capacitor Circuit ； Integrator.

參考文獻

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