應用於高效能酸鹼與葡萄糖生醫感測器之低溫合成鋁摻雜氧化鋅奈米結構之研究

Abstract

氧化鋅係一種極具前瞻性的材料，其具有寬廣的直接帶隙（約3.37電子伏特）、較大的激發態粒子結合能（約60毫電子伏特）、熱穩定性佳，化學穩定性佳，高機械強度…等眾多優點；而由於其奈米結構特有之高表面積與體積比例，氧化鋅將有極大的潛力被應用在生醫感測器上，如離子感測場效電晶體（ISFETs）或延伸式閘極場效電晶體（EGFETs）等元件之感測介面。另一方面，藉由鋁金屬摻雜氧化鋅（AZO）的奈米結構亦已被提出具有高導電性以及高結晶性，而此將完全符合EGFETs對於其感測電極所要求的高導電和低阻抗特性。 在此論文中，本實驗室嘗試將具不同鋁摻雜濃度的AZO奈米結構，利用水熱法的方式在85℃的溫度下成長在AZO/玻璃的表面上。其奈米結構的形態將會隨著鋁摻雜的濃度而有所變化，當其摻雜濃度控制在0~3% 時，所成長出的結構皆為垂直排列的單晶奈米線；當摻雜濃度上升到5% 時，所成長出的則為奈米線與奈米片狀共存的結構；直到摻雜濃度達7% 時，則會全面成長為多晶奈米片狀的結構。實驗結果顯示摻雜濃度控制在3%的AZO奈米線結構表現出最佳的結晶度和較少的結構性缺陷，而由此AZO奈米線所製作出的EGFET敏感膜被應用於pH值的感測時，則表現出較高的電壓感測度（57.95 mV/pH）、較高的電流感測度（0.96 uA1/2/pH）、較佳的線性度（0.9999）、較小的遲滯效應（4.83 mV）、較穩定的時漂效應（1.27 mV/hour）、較低的開路電壓（1.32 V）、並具有更廣泛的感測區間（pH1- pH13）。另一方面，此最佳感測效能的AZO EGFET被應用在葡萄糖的感測上時，於葡萄糖液體濃度0 mM（0 mg/dL）至14 mM（250 mg/dL）的區間內亦具有優異的靈敏度（60.5 uA•cm-2/mM）和線性度（0.9996）。 如此高效能之AZO奈米結構EGFET未來將具有極大的潛力被應用在需要高靈敏度的生醫感測裝置上，其低廉的製造成本亦對於往後的量產過程具有極大的應用價值。

ZnO nanostructures have attracted considerable interests as pH sensors, because of the advantages on thermal stability, chemical stability, and high mechanical strength. The applications include the sensing membranes of ion-sensitive field-effect transistors (ISFETs) or extended-gate field-effect transistors (EGFETs), which are designed for pH value or biotical matters’ concentration determination. On the other hand, the intrinsic ZnO exhibits larger sheet resistance and requires to be doped with group III metal elements (i.e., Al, In, and Ga). To date, however, the low-temperature fabrications of Al-doped ZnO (AZO) nanostructures applied for pH sensors have not been well disclosed. Therefore, a low-temperature (i.e., 85 °C) hydrothermal method was proposed in this work to synthesis the AZO nanostructures on glass substrates. The morphologies of AZO nanostructures were changed from vertically aligned single-crystalline nanowires (NWs), then NWs coexisted with nanosheets (NSs), to complete poly-crystalline NSs in respect of the Al-dosages of 0~3 at.%, 5 at.%, and 7 at.%, correspondingly. The AZO nanostructure with 3 at.% Al-dosages reveals the optimal crystallinity and less structural defects. Consequently, an EGFET’s sensing membrane with such AZO nanostructure exhibited a higher voltage sensitivity of 57.95 mV/pH, higher current sensitivity of 0.96 µA1/2/pH, larger linearity of 0.9999, smaller hysteresis width of 4.83 mV, lower drift rate of 1.27 mV/hour, lower threshold voltage of 1.32 V, small flat band voltage shift, and has a wider sensing range (pH1-pH13). On the other hand, the glucose sensing membrane of AZO pH-EGFETs with Al-dosage of 3 at.% exhibit excellent sensitivity (60.5 µA．cm-2/mM) and linearity (0.9996) from 0 mM (0 mg/dL) to 14 mM (250 mg/dL). Such high performance device possesses a great potential in future biosensor applications, while the low cost nature is also benefiting to future mass productions.