本論文主要是研究氮化鋁鎵/氮化鎵異質結構離子感測場效電晶體，並應用於酸鹼感測之領域。此論文共應用三種方法以提升傳統氮化鋁鎵/氮化鎵異質結構離子感測場效電晶體，分別為過硫酸銨處理、過氧化氫(雙氧水)處理以及利用超音波物化熱裂解法沉積氧化鋁感測薄膜。
為了研究這三種不同方法對於元件表面化學組成、形成薄膜厚度、表面粗糙度、表面親水性與感測薄膜對二維電子雲的影響，因此本論文使用（ㄧ）化學分析電子能譜儀、（二）穿透式電子顯微鏡、（三）原子力顯微鏡、（四）接觸角量測與（五）霍爾量測。透過化學分析電子能譜儀，發現鋁的結合能波峰在應用不同方法後而有所偏移，同時利用定量分析確認所形成的薄膜為氧化鋁。利用穿透式電子顯微鏡，確認不同處理過後所形成的薄膜厚度。透過原子力顯微鏡的觀察，比較不同過硫酸銨處理時間及溫度的表面粗糙度變化。運用接觸角量測技術，觀察元件表面其親水性之變化。利用霍爾量測，比較未處理及應用三種改善方法過後的片電子濃度和電子遷移率。
本論文也製作氮化鋁鎵/氮化鎵金氧半二極體，藉由電容電壓量測計算出透過過氧化氫處理以及超音波物化熱裂解法所形成氧化層薄膜之介電值。同時利用遲滯效應判定表面缺陷密度所改善之幅度，並搭配高低頻法求得其介面狀態密度。
最後，學生製作出氮化鋁鎵/氮化鎵異質結構離子感測電晶體，並分別比較未處理元件、過硫酸銨處理過後元件、過氧化氫處理過後元件以及超音波物化熱裂解法沉積氧化鋁過後的元件等四種元件之酸鹼感測度、反應時間、遲滯效應、穩定度和元件壽命。酸鹼值感測度的部分，令上述元件進行pH2到pH12緩衝溶液的感測，求得其感測度依順序分別為41.6 mV/pH、48.6 mV/pH、55.2 mV/pH及55.6 mV/pH。再來令元件分別接觸 pH7→pH4→pH7 和pH7→pH10→pH7 緩衝溶液，測得元件對於酸鹼值變化的反應時間分別為10.6 秒、9.7秒、7.2秒及6.7秒。接著，我們對於元件進行遲滯效應以及穩定度的探討。遲滯效應的部分，令每個元件依順序接觸 pH7→pH4→pH7→pH10→pH7 和 pH7→pH10→pH7→pH4→pH7 緩衝溶液，算出其遲滯電壓依序分別為11.1 mV、9.6 mV、6.5 mV與5.8 mV。穩定度探討的部分，令每個元件都接觸pH2 、pH7、 pH12三種緩衝溶液長達12小時，觀察其參考電壓的變化來判定其穩定度，以元件放在pH7緩衝溶液中12小時為例，其電壓變化量依序分別為10.1 ∆mV/h、6.3 ∆mV/h、1.91 ∆mV/h以及 1.25 ∆mV/h。最後，我們對於元件壽命進行探討，感測度衰退率分別為 -0.2514 mV/pH∙Day、-0.2386 mV/pH∙Day、-0.1685 mV/pH∙Day 以及 -0.1643 mV/pH∙Day。
實驗結果發現，過硫酸銨處理能夠提升元件的酸鹼值感測度，然而由於無法形成感測薄膜，因此其感測特性並無法媲美其他兩個處理方法。過氧化氫處理能夠有效形成氧化鋁感測薄膜，所花費之時間及成本也為三種方法中最低，然而其成膜均勻性較難控制，因此元件穩定度上不及使用超音波物化熱裂解法的元件。使用超音波物化熱裂解法能夠在非真空環境及低溫(350℃)下沉積高均勻度的氧化鋁感測薄膜，對於元件的酸鹼值感測特性的提升為三種方法中最佳。

This thesis focuses on the investigation of AlGaN/GaN heterostructure Ion-Sensitive Field-Effect-Transistors (ISFETs) and their application for pH sensing. This work provides three kinds of methods, which are (NH4)2S2O8 treatment, hydrogen peroxide (H2O2) treatment and Ultrasonic Spray Paralysis Deposition method, to improve the pH sensing characteristics of the conventional AlGaN/GaN ISFETs.
For the reason to better understand the chemical composition, oxide layer thickness, surface roughness, hydrophilicity and the variation of sheet concentration and mobility of two-dimensional electron gas concentration (2DEG) after applying the methods mentioned above, the (1) Electron Spectroscopy for Chemical Analysis (ESCA), (2) Transmission Electron Microscopy (TEM), (3) Atomic Force Microscopy (AFM), (4) Contact Angle Measurement and (5) Hall Measurement were utilized. By ESCA, we could observe the shift of the binding energy of Al 2p peak after apply those methods. At the same time, we confirmed the formed oxide layers were Al2O3 by quantitative analysis. Next, the thickness of the formed oxide layers could be obtained through TEM. Moreover, by applying AFM, the optimal treatment time and temperature of (NH4)2S2O8 could be acquired. After that, by using Contact Angle Measurement, the hydrophilicity of the samples could be observed. Finally, we could figure out the variation of sheet concentration and mobility of the samples through Hall Measurement.
In addition to material analysis, the Metal-Oxide-Semiconductor (MOS) diodes were also fabricated in this work to figure out k value of the oxide layers, which were formed by H2O2 oxidation and USPD method, from capacitance-voltage measurement. Besides, we also observed the hysteresis of the diodes to confirm the improvement of surface defect density and utilized high-low-frequency method to derive interface state density.
Finally, after the AlGaN/GaN ISFETs were fabricated, we compared the pH sensing characteristics of the untreated device, the device with (NH4)2S2O8 treatment, the device with H2O2 treatments and the device with USPD Al2O3. First of all, the sensitivity of the devices were measured by contacting pH2 ~ pH12 buffer solution. Following the order mentioned above, the sensitivity was 41.6 mV/pH, 48.6 mV/pH, 55.2 mV/pH and 55.6 mV/pH, respectively. Next, the response time of the devices were calculated by contacting buffer solution in the order pH7→pH4→pH7 and pH7→pH10→pH7, which was 10.6 s, 9.7 s, 7.2 s and 6.7 s, respectively. Furthermore, Hysteresis effect and the stability of the devices were investigated. By contacting buffer solution in the order pH7→pH4→pH7→pH10→pH7 and pH7→pH10→pH7→pH4→pH7, the Hysteresis voltages could be obtained, which were 11.1 mV, 9.6 mV, 6.5 mV and 5.8 mV, respectively. As for the stability, by observing the variation of the reference voltage of the devices which were put in pH2, pH7 and pH12 buffer solution over 12 hours, the stability could be determined. For instance, the stability were 10.1 ∆mV/h、6.3 ∆mV/h、1.91 ∆mV/h and 1.25 ∆mV/h respectively in pH7 buffer solution over 12 hours. Finally, the life time of the devices were measured. The decay rate of sensitivity were -0.2514 mV/pH∙Day, -0.2386 mV/pH∙Day, -0.1685 mV/pH∙Day and -0.1643 mV/pH∙Day, respectively.
As the experiment results showed, (NH4)2S2O8 treatment could increase the sensitivity of the device but couldn’t effectively improve other pH sensing characteristics because it could not form sensing film on the surface. On the contrary, H2O2 treatment was able to form Al2O3 sensing film in short time and low cost. However, due to the uniformity problem, the stability of the device with H2O2 treatment was not as good as the device with USPD Al2O3. As for USPD method, it could deposit good uniformity Al2O3 sensing membrane in non-vacuum ambient and low temperature (350℃). Therefore, the improvement of pH sensing characteristics of the device with USPD Al2O3 was the best among all three methods.

[1] P. Bergveld, “Development of an Ion-Sensitive Solid-State Device for Neurophysiological Measurement,” IEEE Trans. Biomed. Eng., vol. BM 17, no. 1, pp. 70-71, Jan. 1970.
[2] P. Bergveld, “Development, Operation, and Application of the Ion-Sensitive Field-Effect Transistor as a Tool for Electrophysiology,” IEEE Trans. Biomed. Eng., vol. BME-19, no.5, pp. 342-351, Sep. 1972.
[3] M. W. Shinwari, M. J. Deen, D. Landheer, “Study of the Electrolyte-Insulator-Semiconductor Field-Effect Transistor (EISFET) with Application in Biosensor Design,” Microelectron. Reliab., vol. 47, pp. 2025-2057, Dec 2007.
[4] M. J. Schoning, M. H. Abouzar, A. Poghossian, “pH and Ion Sensitivity of a Field-Effect EIS (Electrolyte-Insulator-Semiconductor) Sensor Covered with Polyelectrolyte Mutilayers,” J. Solid State Electrochem., vol. 13, pp. 115-122, Jun. 2008.
[5] U. Hashim, S. W. Chong, W. W. Liu, “Fabrication of Silicon Nitride Ion Sensitive Field-Effect Transistor for pH Measurement and DNA Immobilization/Hybridization,” J. Nanomater., vol. 2013, pp. 1-9, Jan. 2013.
[6] L. L. Chi, J. C. Chou, W. Y. Chung, T. P. Sun, S. K. Hsiung, “Study on Extended Gate Field Effect Transistor with Tin Oxide Sensing Membrane,” Mater. Chem. Phys., vol. 63, pp. 19-23, Feb. 2000.
[7] G. Steinhoff, M. Hermann, W. J. Schaff, L. F. Eastman, M. Stutzmann, M. Eickhoff, “pH Response of GaN Surfaces and Its Application for pH-Sensitive Field-Effect Transistors,” Appl. Phys. Lett., vol. 83, no. 1, pp. 177-179, Jul. 2003.
[8] M. Stutzmanna, G. Steinhoffa, M. Eickhoffa, O. Ambachera, C.E. Nebela, J. Schalwigb, R. Neubergerb, G. Müllerb, “GaN-Based Heterostructure for Sensor Applications,” Diam. Relat. Mater., vol. 11, pp. 886-891, Mar. 2002.
[9] G. Steinhoff, O. Purrucker, M. Tanaka, M. Stutzmann1, M. Eickhoff, “AlxGa1–xN—A New Material System for Biosensors,” Adv. Funct. Mater., vol. 13, pp. 841-846, Nov. 2003.
[10] B. S. Kang, S. Kim, F. Ren, B. P. Gila, C. R. Abernathy, and S. J. Pearton, “AlGaN/GaN-Based Diodes and Gateless HEMTs for Gas and Chemical Sensing,” IEEE Sensor J., vol. 5, pp. 677-680, Aug. 2005.
[11] T. Kokawa, T. Sato, H. Hasegawa, T. Hashizume, “Liquid-Phase Sensors Using Open-Gate AlGaN/GaN HEMT Structure,” J. Vac. Sci. Technol. B, vol. 24, pp. 1972-1976, Jul.2006.
[12] J. P. Ibbetson, P. T. Fini, K. D. Ness, S. P. DenBaars, J. S. Speck, U. K. Mishra, ” Polarization Effects, Surface States, and the Source of Electrons in AlGaN/GaN Heterostructure Field Effect Transistors,” Appl. Phys. Lett., vol. 77, no. 2, pp. 250-252, Jul. 2000.
[13] D. L. Harame, L. J. Bousse, J. D. Shott, J. D. Meindl, “Ion-Sensitive Devices with Silicon Nitride and Borosilicate Glass Insulator,” IEEE Trans. Electron Devices, vol. ED 34, pp. 1700-1707, Aug. 1987.
[14] L. Bousse, H. H. Vandenvlekkert, and N. F. Deroij, “Hysteresis in Al2O3-Gate ISFETs,” Sens. Actuator B-Chem., vol. 2, no. 2, pp. 103-110, May 1990.
[15] B. S. Kang, H. T. Wang, F. Ren, B. P. Gila, C. R. Abernathy, S. J. Pearton, J. W. Johnson, P. Rajagopal, J. C. Roberts, E. L. Piner, and K. J. Linthicum, “pH sensor Using AlGaN/GaN High Electron Mobility Transistors with Sc2O3 in the Gate Region,” Appl. Phys. Lett., vol. 91, no. 1, pp. 012110-1-012110-3, Jul. 2007.
[16] J. L. Chiang, Y. C. Chen, and J. C. Chou, “Simulation and Experimental Study of the pH-Sensing Property for AlN Thin Films,” Jpn. J. Appl. Phys., vol. 40, no. 10, pp. 5900-5904, Oct. 2001.
[17] T. Matsuo, M. Esashi, H. Abe, “pH-ISFET’s Using Al2O3, Si3N4, and SiO2 Gate Thin Films,” IEEE Trans. Electron Devices, vol. ED 26, pp. 1856-1857, Aug. 1979.
[18] T. F. Lu, H. C. Chuang, J. C. Wang, C. M. Yang, P. C. Kuo, C. S. Lai, “Effects of Thickness and Rapid Thermal Annealing on pH Sensing Characteristics of Thin HfO2 Films Formed by Atomic Layer Deposition,” Jpn. J. Appl. Phys., vol. 52, 10PG03, Oct. 2011.
[19] T. M. Pan, K. M. Liao, “Structural Properties and Sensing Characteristics of Y2O3 Sensing Membrane for pH-ISFET,” Sens. Actuat. B, vol. 127, pp. 480-485, May 2007.
[20] A. Eftekhari, “pH Sensor Based on Deposited Film of Lead Oxide on Aluminum Substrate Electrode,” Sens. Actuat. B, vol. 88, pp. 234-238, Feb. 2003.
[21] P. Shuk and K. V. Ramanujachary, “New Metal-Oxide-Type pH Sensors,“ Solid State Ion., vol. 86-88, pp. 1115-1120, Jul. 1996.
[22] D. E. Yates, S. Levine, T. W. Healy, “Site-Binding Model of the Electrical Double Layer at the Oxide/Water Interface,” J. Chem. Soc., Faraday Trans. 1, vol. 70, pp. 1807-1818, Jan. 1974.
[23] Y. H. Chang, Y. S. Lu, Y. L. Hong, S. Gwo, J. A. Yeh, “Highly Sensitive pH Sensing Using an Indium Nitride Ion-Sensitive Field Effect Transistor,” IEEE Sens. J., vol. 11, pp.1157-1161, May 2011.
[24] C. D. Fung, P. W. Cheung, W. H. Ko, “A Generalized Theory of an Electrolyte-Insulator-Semiconductor Field-Effect Transistor,” IEEE Trans. Electron Devices, vol. ED 33, pp. 8-18, Jan. 1986.
[25] H. K. Liao, L. L. Chi, J. C. Chou, W. Y. Chung, T. P. Sun, S. K. Hsiung, “Study on pHpzc and surface potential of tin oxide gate ISFET,” Mater. Chem. Phys., vol. 59, pp. 6-11, Apr. 1999.
[26] S. R. Morrison, Electrochemistry at Semiconductor and Oxidized Metal Electrodes, Springer, New York, America, Nov. 1980.
[27] A. A. Kornyshev, “Double-Layer in Ionic Liquids: Paradigm Change?” J. Phys. Chem. B, vol. 111, pp. 5545-5557, May 2007.
[28] K. B. Oldham, “A Gouy-Chapman-Stern Model of the Double Layer at a (Metal)/(Ionic Liquid) Interface,” J. Electroanal. Chem., vol. 613, pp. 131-138, Feb. 2008.
[29] P. Bergveld, “Thirty years of ISFETOLOGY: What happened in the past 30 years and what may happen in the next 30 years,” Sens. Actuat. B, vol. 88, pp. 1-20, Jan. 2003.
[30] P. Bergveld, A. Sibbald, Analytical and Biomedical Applications of Ion-Selective Field-Effect Transistors, Elsevier Science Publishing Company Inc., New York, America, Chapter 2~3, Jan. 1988.
[31] J. B. Mooney and S. B. Radding, “Spray Pyrolysis Processing,” Ann. Rev. Mater. Sci., vol. 12, pp. 81-101, 1982.
[32] M. C. Rhoten and T. C. Devore, “Evolved Gas Analysis Investigation of the Reaction between Tris(2,4-pentanedionato)aluminum and Water Vapor in Chemical Vapor Deposition Processes To Produce Alumina,” Chem. Mater., vol. 9, pp. 1757-1764, Aug. 1997.
[33] I. M. Kolthoff, I. K. Miller, “The Chemistry of Persulfate. I. The Kinetics and Mechanism of the Decomposition of the Persulfate Ion in Aqueous Medium,” J. Am. Chem. Soc., vol. 73, pp. 3055-3059, Jul. 1951.
[34] B. G. Yacobi, “Semiconductor Materials: An Introduction to Basic Principles,” Kluwer Academic, Jan. 2003.
[35] J. C. Vickerman, I. S. Gilmore, “Surface Analysis : The Principle Techniques, 2nd Edition,” John Wiley & Sons, Ltd, Mar. 2009
[36] C. D. Wagner, W. M. Riggs, L. E. Davis, J. F. Moulder, G. E. Muilenberg, “ Handbook of X-Ray Photoelectron Spectroscopy,” Perkin-Elmer Corp., 1979
[37] D. Y. Kwok, A. W. Neumann, “Contact Angel Measurement and Contact Angle Interpretation,” Adv. Colloid Interface Sci., vol. 81, pp. 167-249, Sep. 1999.
[38] C. Kittel, “Introduction to Solid State Physics, 8th edition,” John Wiley & Sons, Ltd, Oct. 2005.
[39] J. Antoszewski, M. Gracey, J. M. Dell, L. Faraone, T. A. Fisher, G. Parish, Y. F. Wu, U. K. Mishra, “Scattering Mechanisms Limiting Two-Dimensional Electron Gas Mobility in Al0.25Ga0.75N/GaN Modulation-Doped Field-Effect-Transistors,” J. Appl. Phys., vol. 87, pp. 3900-3904, Apr. 2000.
[40] H. Y. Liu, B. Y. Chou, W. C. Hsu, C. S. Lee, C. S. Ho, “A Simple Gate-Dielectric Fabrication Process for AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistors,” IEEE Electron Device Lett., vol. 33, pp. 997-999, Jul. 2012.
[41] F. Schwierz, J. J. Liou, “Modern Microwave Transistors,” John Wiley & Sons, Inc., pp. 237-239, Dec. 2002.
[42] W. Lu, V. Kumar, R. Schwindt, E. Piner, I. Adesida, “A Comparative Study of Surface Passivation on AlGaN/GaN HEMTs,” Solid State Electron., vol. 46, pp. 1441-1444, Sep. 2002.
[43] Y. Yue, Y. Hao, J. Zhang, J. Ni, W. Mao, Q. Feng, L. Liu, “AlGaN/GaN MOS-HEMT with HfO2 Dielectric and Al2O3 Interfacial Passivation Layer Grown by Atomic Layer Deposition,” IEEE Electron Device Lett., vol. 29, pp. 838-840, Aug. 2008.
[44] C. Mizue, Y. Hori, M. Miczek, T. Hashizume, “Capacitance-Voltage Characteristics of Al2O3/AlGaN/GaN Structures and State Density Distribution at Al2O3/AlGaN Interface,” Jpn. J. Appl. Phys., vol. 50, pp. 021001, Feb. 2011.
[45] C. T. Lee, Y. S. Chiu, X. Q. Wang, “Performance Enhancement Mechanisms of Passivated InN/GaN-Heterostructured Ion-Selective Field-Effect-Transistor pH Sensors,” Sens. Actuat. B, vol. 181, pp. 810-815, May. 2013.
[46] M. S. Z. Abidin, A. M. Hashim, M. E. Sharifabad, S. F. A. Rahman, T. Sadoh, “Open-Gated pH Sensors Fabrication on an Undoped-AlGaN/GaN HEMT Structure,” Sensors, vol. 11, pp. 3067-3077, Mar. 2011.
[47] S. H. Ryu, S. K. Lee, Y. S. Sohn, W. H. Son, S. Y. Choi, “Characteristics of Al2O3 Gate pH-ISFET Difference of Thermal Annealing Temperature,” Biomed. Eng. App. Bas. C., vol. 24, pp. 117-121, Feb. 2012.
[48] T. M. Pan, M. D. Huang, “Structural Properties and Sensing Characteristics of High-k Ho2O3 Sensing Film-Based Electrolyte-Insulator-Semiconductor,” Mater. Chem. Phys., vol. 129, pp. 919-924, Oct. 2011.
[49] A. Bengoechea-Encabo, J. Howgate, M. Stutzmann, M. Eickhoff, M. A. Sanchez-Garcia, “Ultrathin GaN/AlN/GaN Solution-Gate Field Effect Transistor with Enhanced Resolution at Low Source-Gate Voltage,” Sens. Actuat. B, vol. 142, pp. 304-307, Oct. 2009.
[50] T. Brazzini, A. Bengoechea-Encabo, M. A. Sanchez-Garcia, F. Calle, “Investigation of AlInN Narrier ISFET Structures with GaN Capping for pH Detection,” Sens. Actuat. B, vol. 176, pp. 704-707, Jan. 2013.
[51] S. Jamasb, S. Collins, R. L. Smith, “A Physical Model for Drift in pH ISFETs,” Sens. Actuat. B, vol. 49, pp. 146-155, Jun. 1998.
[52] S. Milenkovic, V. Dalbert, R. Marinkovic, A. W. Hassei, “Selective Matrix Dissolution in an Al–Si Eutectic,” Corros. Sci., Vol. 51, pp. 1490-1495, Jul. 2009.
[53] L. Bousse, S, Mostarshed, “Comparison of the Hysteresis of Ta2O3 and Si3N4 pH-Sensing Insulators,” Sens. Actuat. B, Vol. 17, pp. 157-164, Jan. 1994.
[54] T. M. Pan, J. C. Lin, M .H. Wu, C. S. Lai, “Study of High-k Er2O3 Thin Layers as ISFET Sensitive Insulator Surface,” Sens. Actuat. B, Vol. 138, pp. 619-624, May. 2009.
[55] T. M. Pan, K. M. Liao, “Development of a High-k Pr2O3 Sensing Membrane for pH-ISFET Application,” IEEE Sens. J., Vol. 8, pp. 1856-1861, Nov. 2008.
[56] D. Yun, Y. D. Wang, G. H. Wang, “Time-Dependent Response Characteristics of pH-Sensitive ISFET,” Sens. Actuat. B, vol. 3, pp. 279-285, Apr. 1991.
[57] Zhong Yule, Zhao Shouan, Lin Tao, “Drift Characteristics of pH-ISFET Output,” Chin. J. Semiconduct., vol. 12, pp. 838-843, Dec.1994.
[58] S. Jamasb, S. D. Collins, R. L. Smith, “A Physical Model for Threshold Voltage Instability in Si3N4-Gate H+-Sensitive FET’s (pH-ISFETs),” IEEE Trans. Electron Devices, vol. 45, pp. 1239-1245, Jun. 1998.