Effect of gate dielectric on the performance of ISFET with SU-8 encapsulation

  • S. Dawnee
  • Navakanta Bhat
Original Paper


The design and fabrication of open gated ISFETs with different gate dielectric is reported. A comparative analysis of three different sensing layers SiO2, SiO2/Si3N4 stack and SiO2/Al2O3 stack is presented. The focus is on the simple fabrication technique, SU-8 encapsulation and its application as a pH sensor. The SU-8 encapsulation process is developed for the creation of liquid well to enable efficient interaction with biological fluid. For pH analysis the ISFET was tested in buffer solutions with different pH values. A platinum wire was used as the reference electrode for liquid gating. The pH response is evaluated from the IV characteristics and ISFETs with SiO2/Si3N4 stack and SiO2/Al2O3 stack showed better pH response with sensitivity of 59.33 mV/pH and 55.68 mV/pH, respectively as against sensitivity of 48.9 mV/pH in ISFETs with SiO2.


Ion sensitive field effective transistors (ISFET) SU-8 encapsulation pH Sensor 


  1. Abramova N, Bratov A (2009) Photocurable polymers for ion selective field effect transistors—20 years of applications. Sensors 9:7097–7110. ISSN 1424-8220CrossRefGoogle Scholar
  2. Bergveld P (1972) Development, operation, and application of the ion-sensitive field-effect transistor as a tool for electrophysiology. IEEE Trans Bio-Med Eng 19(5):342–351CrossRefGoogle Scholar
  3. Bergveld P (2003) Thirty years of ISFETOLOGY what happened in the past 30 years and what may happen in the next 30 years. Sens Actuators B 88(1):1–20CrossRefGoogle Scholar
  4. Bergveld P, Van Hal R, Eijkel J (1995) The remarkable similarity between the acid base properties of ISFETs and proteins and proteins and the consequences for the design of ISFET biosensors. Biosens Bioelectron 10:405–414CrossRefGoogle Scholar
  5. Chang SR, Chang CH, Lin JS, Lu MS, Lee YT, Yeh SR, Chen H (2008) Die-level post CMOS processes for fabricating open-gate field effect biosensor arrays with on chip circuitry. J Micromech Microeng 18(11):115032CrossRefGoogle Scholar
  6. Chou JLCJC, Chen YC (2001) Study of the pH ISFET and EnFET for biosensor applications. J Med Biol Eng 21(3):135–146Google Scholar
  7. Dumschat C, Muller H, Rautschek H, Timpe H-J (1990) Encapsulation of chemically sensitive field-effect transistors with photocurable epoxy resins. Sens Actuators B 2:271–276CrossRefGoogle Scholar
  8. Kal S, Bhanupriya V (2008) Design and modelling of ISFET for pH sensing. In: TENCON 2007–2007 IEEE Region 10 ConferenceGoogle Scholar
  9. Khanna VK (2012) Fabrication of ISFET microsensor by diffusion based Al gate NMOS process and determination of its pH sensitivity from transfer characteristics. Indian J Pure Appl Phys 50:199–207Google Scholar
  10. Kim DS, Jeong YT, Park HJ, Shin JK, Choi P, Lee JH, Lim G (2004) An FET-type charge sensor for highly sensitive detection of DNA sequence. Biosens Bioelectron 20(1):69–74CrossRefGoogle Scholar
  11. Li DC, Yang PH, Lu MS (2010) CMOS open-gate Ion-Sensitive Field—Effect Transistors for Ultrasensitive Dopamine detection. IEEE Trans Electron Dev 57(10):2761–2767CrossRefGoogle Scholar
  12. Ortiz Conde A, Garca Sanches F, Lio JJ, Cardeira A, Estrada M, Yue Y (2002) A review of recent MOSFET threshold voltage extraction methods. Microelectron Reliab 42:583–596CrossRefGoogle Scholar
  13. Palan B, Roubik K, Husak M, Courtois B (2000) CMOS ISFET based structures for Biomedical Applications. In: IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine and BiologyGoogle Scholar
  14. Van Hal R, Eijkel J, Bergveld P (1995) A novel description of ISFET sensitivity with the buffering capacity and double layer capacitance as key parameters. Sens Actuators B 24(1):201–205Google Scholar
  15. Waleed Shinwari M, Jamal Deen M, Landheer Dolf (2007) Study of the electrolyte-insulator-semiconductor field-effect transistor (EISFET) with applications in biosensor design. Microelectron Reliab 47(12):2025–2057CrossRefGoogle Scholar
  16. Zafar S, D’Emic C, Afzali A, Fletcher B, Zhu Y, Ning T (2011) Optimization of pH sensing using silicon nanowire field effect transistors with HfO2 as the Sensing surface. Nanotechnology 22:405501CrossRefGoogle Scholar

Copyright information

© Institute of Smart Structures & Systems, Department of Aerospace Engineering, Indian Institute of Science, Bangalore, India 2018

Authors and Affiliations

  1. 1.Department of Electrical Communication EngineeringIndian Institute of ScienceBangaloreIndia
  2. 2.Centre for Nano Science and EngineeringIndian Institute of ScienceBangaloreIndia
  3. 3.Department of Electrical and Electronics EngineeringRamaiah Institute of TechnologyBangaloreIndia

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