二氧化鋯作為閘極之離子感測場效電晶體應用在pH量測之最佳化退火製程研究

Abstract

離子感測場效電晶體(Ion-Sensitive Field Effect Transistor, ISFET)首先是在1970年由P. Bergveld提出。其主要與傳統的MOSFET結構之差異，就是把金屬閘極換成感測層以及將絕緣層暴露在電解液中。另外ISFET擁有許多優點，像是成本低、尺寸小、輸出阻抗低、輸入阻抗高、響應時間快，因此非常適合應用在生物感應器上。 我們在研究pH-ISFET的應用上時靈敏度是一個重要關鍵的因素。除此之外還有限制了pH-ISFET應用的重要因素遲滯和漂移。為了得到高的靈敏度和低的漂移以及遲滯，許多的感測層材料像是SiO2, Al2O3, Si3N4 和Ta2O5都被提出來研究。在本篇論文中我們選擇二氧化鋯當作感測層去研究不同的退火溫度對於pH-ISFET的影響。 在本篇研究中，我們藉由研究靈敏度、遲滯和漂移來找出二氧化鋯作為閘極pH-ISFET之最佳的退火溫度。從實驗的結果我們可以發現在600℃的退火溫度有最大的靈敏度54.5 mV/pH和最小的漂移速率0.54 mV/h。另外在600℃的退火溫度下遲滯也最小。遲滯在迴圈pH = 7-3-7-11-7比迴圈在pH = 7-11-7-3-7小，大小分別為1.43和5.45 mV。我們也看到遲滯在酸的迴圈比在鹼的迴圈小造成了不對稱的遲滯結果。 從高的靈敏度、小的遲滯和低的漂移速率結果，我們可以推斷出最佳的退火溫度是在600℃。因此以二氧化鋯作為閘極的pH-ISFET 在600℃退火條件下非常適合應用在pH量測上。

The ion-sensitive field effect transistor (ISFET) was first reported by P. Bergveld in 1970s. In comparison to a conventional MOSFET structure, the metal gate is replaced by the sensing layer and exposing the insulator to the electrolyte. There are many advantages for the ISFET, such as, low cost, small size, low output impedance, high input impedance, and rapid response. Therefore, it’s very suitable for the biosensor applications. The sensitivity is a key factor for the application of pH-ISFETs. On the side, the hysteresis and drift are the most important factors that prohibit the application of the pH-ISFETs. In order to obtain high sensitivity, low drift and hysteresis, many pH-sensitive materials, such as, SiO2, Al2O3, Si3N4 and Ta2O5 have been investigated. In this thesis, we choose ZrO2 as the sensing film and investigate the influences of different annealing temperatures on the ZrO2 sensing film for the pH-ISFET. In this study, we find the optimal annealing temperature by investigating sensitivity, hysteresis and drift for ZrO2 gate pH-ISFET. Form the experimental results, we can find that annealing temperature of 600℃ has a maximal sensitivity of 54.5 mV/pH and minimal drift rate of 0.54 mV/h. In addition, the annealing temperature of 600℃ also shows the smallest hysteresis. The hysteresis in pH loop 7-3-7-11-7 is smaller than that in pH loop 7-11-7-3-7, with the magnitude of 1.43 and 5.45 mV, respectively. We also observe that the hysteresis of the acid side is smaller than basic side, results in asymmetric hysteresis. From the result of high pH-sensitivity, small hysteresis and low drift, we can conclude the optimal annealing temperature is around 600℃. It reveals that ZrO2 gate pH-ISFET annealed at 600℃ is suitable for pH measurement.