場效電晶體式微懸臂樑感測器於力學特性與溫度效應之研究

Abstract

近幾年隨著生物技術及微系統的發展，各國社會趨勢逐漸走向高齡化，醫療資源的需求日益增大。有別於傳統相形笨重和高成本且速度緩慢之檢驗設備，一種具有微小化、可攜式、高靈敏度、少量檢體、免螢光標定以及具快速檢測的生物晶片，已經成為生物領域、微機電領域一重要指標性研究發展方向。 本論文利用微機電技術與半導體技術製作出以多晶矽薄膜場效電晶體作為訊號轉換機制的微懸臂樑感測器。本研究所製作出薄膜電晶體之電子遷移率為30~34cm2/Vs，並利用力學為基礎於固定VG=7V探討感測元件最佳靈敏度為0.034μA/μm。本研究所作之薄膜場效電晶體(CONTROL)與薄膜場效電晶體式微懸臂樑(TFT-MCL)受溫度效應時的電流變化(ΔI/ΔT)分別為0.51μA/℃與0.60μA/℃，可以發現薄膜電晶體受溫度效應影響十分顯著。將其分別對載子遷移率(Mobility)、臨限電壓(Threshold Voltage)、汲極電流(ID-VD) 於溫度效應下作研究。由研究結果，在薄膜場效電晶體式微懸臂樑與控制組溫度效應中，發現載子遷移率隨溫度上升而增加、臨限電壓趨勢雖然相同，對溫度的靈敏度分別有1.45倍與0.76倍的差距存在。藉由ID-VD實驗發現飽和電流訊號受溫度效應影響的變化，在控制組與場效電晶體式微懸臂樑上的變化量是不同的，將其微懸臂樑溫度效應分別於力學特性、熱傳特性、電特性做研究探討。實驗結果發現到其主要分別來自電阻熱效應(Temperature Coefficient of Resistance)佔74%、雙膜效應(Bimorph Effect)佔1%、熱消散效應(Heat Dissipation Effect)佔9%以及微懸臂樑之起始翹曲不同所造成的本質溫度效應差異(Initial Deformation Induced Variation of Temperature Effect)佔16%，由實驗結果發現溫度效應於微懸臂樑在訊號量測時，造成訊號值誤判的可能性很高，故探討溫度效應補償的可行性。 本論文最後利用溫度補償方法，將上述所列出微懸臂樑溫度效應之因素，利用控制組當作補償參照組來扣除微懸臂樑之溫度效應。研究結果顯示經過溫度補償後，可將微懸臂樑受溫度效應影響減少約60倍。應用在單點負荷施加於微懸臂樑上，並用溫度補償將溫度效應消除，得到單點負荷真實訊號值。此溫度補償方法優點是不論是在溫差範圍多大情況下，皆可進行溫度效應之補償，此補償方法讓薄膜場效電晶體式微懸臂樑感測器不需要龐大的恆溫儀器。因此溫度補償機制的研究，無疑的對於感測儀器是一重大的貢獻。本實驗所使用之方法非常簡易，將對薄膜場效電晶體式微懸臂樑的穩定性與應用面有所提升，並期許對於微流道生醫晶片或其他領域，存在溫度效應相關問題的，能有所助益。

In recent year, with the development of biotechnology and microsystems, the aging society is gradually coming. Portable biosensors offer advantages over conventional instruments on miniaturization, label-free feature, portability, real-time rapid diagnosis, and potential low cost, showing the direction of research and development. This study successfully utilized thin-film transistor(TFT) as a sensing transducer to convert induced stresses of a microcantilever(MCL) sensor. The thin-film transistor–based microcantilever(TFT-based MCL) was fabricated by semiconductor and micro-electromechanical system(MEMS) fabrication technology. Meanwhile, the mobility of the TFT device was measured to be 30~34 cm2/Vs, and the sensitivity of TFT-based MCL device was 0.034 μA/μm. For sensing purpose of the TFT-based MCL sensor, the device was very sensitive to temperature effect, which induced a result of a considerable current change. The sensitivity of the TFT-based MCL for temperature to saturation current was measured to be 0.6 μA/℃. In addition, the temperature effect induced changes of mobility and threshold voltage simultaneously. By the test of ID-VD with respect to temperature effect, five major factors were found to play considerable roles in the TFT-based MCL, including temperature coefficient of resistance of 74%, bimorph effect of about 1%, heat dissipation of 9%, and initial residual stress deformation-induced variation of temperature effect of 15%. Finally, this study utilized a fixed TFT on a substrate as temperature sensor for thermal effect compensation to eliminate the temperature effect of the TFT-based MCL. The temperature feedback has been proved to demonstrate the device with a large scale of temperature variation. As a result, the TFT-based MCL sensor has been expected for biochemical detection with the elimination of temperature-sensitive effect.