用於生物感測的新型多晶矽薄膜電晶體之研究

Abstract

隨著生物醫學半導體技術的發展進步，許多研究開始探討將金氧半場效電晶體(MOSFET)結構應用在可量測酸鹼值的離子感測器上，但是這些研究都使用單晶矽作為離子感測器的載子通道，而非多晶矽的載子通道。我們成功利用低溫多晶矽薄膜電晶體製程延伸應用至離子與生物感測器上，結合不同製程方式與結構，達到不同的應用目標與改善。而且我們是利用傳統的二氧化矽材料當作感測薄膜，其擁有低成本、高產量和簡單的製程優點。 首先低溫多晶矽薄膜電晶體元件的離子感測度可以透過氫氣熱退火製程改善表面二氧化矽薄膜的材料特性，進而使離子感測度改善，低溫多晶矽薄膜電晶體感測器經過氫氣熱退火比沒有經過氫氣熱退火製程有高的離子感測度，這是因為在氧化層內的氫原子減少了矽的空鍵和增加了矽氫氧和矽氧鍵結使得產生額外的表面活化鍵結，這些鍵結使化學反應增加。隨後，參考電極-氧化層-氮化層-氧化層-多晶矽薄膜電晶體離子選擇感測器第一次被提出，利用電壓使電子注入到氮化矽中的奈米矽中，使氫離子因為電子儲存在奈米矽中而使吸附在感測膜上更佳，進而展現出高的酸鹼敏感度。 第二，我們探討在雙閘極多晶矽離子感測器擁有不同離子感測膜之厚度時對於上方液態參考電極以及下方底部閘極的酸鹼敏感度之影響。最重要的是，我們發現多晶矽薄膜電晶體元件的感測度會隨者感測薄膜的厚度增加而降低，而遲滯電壓和長時間飄移現象也會相對的降低，這改善的原因是因為我們使用較厚的感測度厚度時會使閘極電容(CSens)變小，這將使得上方與下方電容的比例下降，所以可以使多晶矽離子感測器展現出較穩定的遲滯和飄移現象。 最後，利用符合互補式金屬氧化物半導體製程的側壁技術開發出新穎的牛角型多晶矽奈米線生物感測器，此元件可以偵測酸鹼值以及生物分子並擁有低成本與高感測度的特點，牛角型多晶矽奈米線是利用梯型形狀的假閘極蝕刻技術和側壁技術製作而成，我們利用牛角型狀的尖端處會使電場變大的現象找出最大的電流變化是在閘極電壓為二伏特和三伏特，此時是最好的即時電流變化量區域，此外這個特殊的特性很適合製作和應用到生物分子感測器元件。我們提出一個新的方法就是利用牛角型奈米線的電流去感測酸鹼值和生物分子，我發現電流變化百分率可以超過百分之三十五，我們也利用這個感測器的反應對鐵蛋白抗原的存在做了研究。

As the development of the biomedical semiconductor technology, the metal-oxide-silicon field-effect transistor (MOSFET) structure applied on pH sensing of ISFET (Ion-Selective-Field-Effect-Transistor) has been researched in several studies. However, all the researches of ISFET above were based on single crystalline silicon channel rather than poly-Si channel film. We successfully fabricated and demonstrated low temperature poly-Si (LTPS) thin film transistor (TFT) that extended to use in the ion sensitive device and biosensors, respectively. In order to achieve the different application targets and improved electrical characteristics, we combine the different processes and structures. Furthermore, we use the traditional gate oxide material such as silicon oxide to be the sensing membranes that have the advantages of low cost, high throughput, and simple process. First, we report an improvement in the pH sensitivity of LTPS TFT sensors using an H2 sintering process. The LTPS TFT sensors with H2 sintering exhibited a high sensitivity than that without H2 sintering. This result may be due to the resulting increase in the number of Si–OH2+ and Si–O− bonds due to the incorporation of H in the gate oxide to reduce the dangling silicon bonds and hence create the surface active sites and the resulting increase in the number of chemical reactions at these surface active sites. On the other hand, the RONOS (Reference electrode-Oxide- Nitride-Oxide poly-Si) TFT ISFET can achieve excellent properties in pH sensing due to the hydrogen ion attraction by trapped electrons with silicon nitride embedded nanocrystals when applying a stress voltage for the first time. Second, we investigated on the pH sensitivity of the liquid-gate and bottom-gate by utilizing a DG poly-Si TFT with various sensing membrane thicknesses as a pH-ISFET. Most importantly, the pH sensitivity of poly-Si ISFET device decreases with increasing the sensing film thickness, whereas hysteresis voltage and drift rate decrease accordingly. An improved hysteresis phenomenon and drift behavior can be construed as that the CSens could become smaller with the thicker sensing membrane, which leads to the decrease in the capacitance ratio between top and bottom gate oxides. As a result, the poly-Si ISFET exhibits the stable hysteresis and drift. Finally, the novel horn-like poly-Si nanowires biosensors have been developed by using spacer technology that is complementary metal-oxide-semiconductor (CMOS) compatible for pH and bimolecular detection with low cost and high sensitivity. The horn-like structure was fabricated by trapezoidal-shape dummy gate etching technology and the spacer technology. We use the phenomenon that the horn-like sharp inducing a strong electrical field to find a largest difference of the drain current between liquid gate voltage at 2V and 3V as the best real time sensing condition. A new method for detection of pH and biomolecule from current of horn-like nanowires structure is suggested. The obtained percentage of signal was over 35 %. Moreover, the sensor response to the presence of ferritin antigen was also investigated.