奈米碳管與切換電容式放大器整合為氣體感測器之研究

A Study on the integration of Carbon nanotubes with Switched-Capacitor Amplifier into a Gas Sensor

楊耀沂(Yao-Yi Yang)

指導教授 ： 黃榮堂

國立臺北科技大學/機電學院/機電整合研究所/碩士(2007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阻抗量測單元或電流量測單元，因此能夠直接量測、判斷所測得的微量電訊變化。
此訊號讀出電路須具備高精確度和對微小訊號的讀出能力，以確保其高靈敏度的偵測能力。由於奈米碳管在感測氣體時，訊號大部分為nA~μA等級的電流訊號，因此，此放大電路目標為偵測到數十~數百nA的訊號變化量，再將其放大可直接進行讀取的訊號範圍。
有鑑於一般轉導放大器不敷使用，本研究選擇切換電容式放大器作為訊號的讀出電路。架構上，利用兩級的方式，第一級為切換電容式積分器，將電流訊號轉為電壓訊號，再經由第二級的切換電容式放大級將訊號再一次放大。此外，由於切換電容式電路容易受到其運算放大器的非理想特性所影響，本研究也針對輸入偏移電壓以及低頻雜訊做修正，利用相關雙取樣技術應用在切換電容式電路上，可以解決上述的問題。
未來此感測元件可於奈米碳管表面進行改質，藉此可以偵測不同的氣體分子，將可提供未來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。
本研究所使用的製程設計條件，乃透過國家晶片中心(CIC)，由台灣積體電路製造公司(TSMC)所提供 0.35μm 2P4M製程為主。

關鍵字

奈米碳管 ； 氣體感測器 ； CMOS ； 切換電容放大器 ； 相關雙取樣

並列摘要

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.

並列關鍵字

Carbon Nanotubes (CNTs ； gas sensor ； CMOS ； Switched-Capacitor Amplifier ； Correlated-Double Sampling (CDS)

參考文獻

〔1〕 蔡政宏,” 奈米碳管電子元件之製備與應用”,國立台北科技大學機電整合研究所碩士論文,2006年

〔3〕 林良澤,” 與CMOS製程相容之奈米碳管場效電晶體氣體感測元件之研究”, 國立台北科技大學機電整合研究所碩士論文,2007年

〔4〕 Zhi-Bin Zhang, Xian-Jie Liu, Eleanor E. B. Campbell, Shi-Li Zhang. “ Alternating current dielectrophoresis of carbon nanotubes. J. Appl. Phys., Vol.98,056103,2005

〔5〕 Ralph Krupke, Frank Hennrich ,et. al.. “Separation of Metallic from semiconducting Single-Walled Carbon Nanotubes”. Science, Vol.301, p.344-347, 2003, July.

〔6〕 Sedra / Smith, “Microelectronic Circuits”, OXFORD 4th Edition.