Sensors and Actuators B 151 (2010) 39–55 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Review Advances of SiC-based MOS capacitor hydrogen sensors for harsh environment applications Mun Teng Soo a,b , Kuan Yew Cheong a,b,∗ , Ahmad Fauzi Mohd Noor b a Energy Efficient & Sustainable Semiconductor Research Group (esReG), Malaysia b School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, Seri Ampangan, 14300 Nibong Tebal, Pulau Pinang, Malaysia article info Article history: Received 6 April 2010 Received in revised form 29 August 2010 Accepted 25 September 2010 Available online 23 October 2010 Keywords: Silicon carbide (SiC) MOS capacitor Hydrogen sensor Harsh environment Metal electrode Dielectric layer abstract SiC-based hydrogen sensors have attracted much attention due to applications in harsh environments. In this paper, harsh environment is defined. Characteristics of SiC-based hydrogen sensors for harsh environment applications are reviewed. Various types of SiC-based field effect hydrogen sensor in terms of their respective history, structure, advantages and disadvantages have been discussed. SiC-based MOS capacitor hydrogen sensor will be conferred in detail. The reasons for selecting SiC in fabricating MOS capacitor hydrogen sensor for harsh environment applications are elucidated. Different hydrogen sensing mechanisms depend on the temperatures and the conditions of catalytic metal layer are highlighted. MOS capacitor SiC-based sensors fabricated by previous research groups are listed. Each catalytic electrodes and oxide layers selected have their significant properties. Examples of nanostructured materials that have been used in forming oxide layer are illustrated. The future challenges in terms of material (metal electrodes and oxide layers) properties and surface properties of materials are described. It is concluded that MOS capacitor SiC-based hydrogen sensors promote green technology. © 2010 Elsevier B.V. All rights reserved. Contents 1. Introduction .......................................................................................................................................... 40 2. SiC-based hydrogen sensor for harsh environment applications ................................................................................... 40 2.1. The selection of SiC ........................................................................................................................... 42 2.2. SiC polytypes ................................................................................................................................. 42 2.3. Characteristics of SiC-based hydrogen sensor ............................................................................................... 43 2.4. Types of SiC-based field-effect hydrogen sensor ............................................................................................ 43 2.4.1. MOS capacitors ..................................................................................................................... 44 2.4.2. Schottky diodes ..................................................................................................................... 44 2.4.3. p–n junction diodes ................................................................................................................. 45 2.4.4. MOS field-effect transistors (MOSFETs) ............................................................................................ 45 3. SiC-based MOS capacitor hydrogen sensor .......................................................................................................... 46 3.1. Hydrogen sensing mechanisms .............................................................................................................. 46 3.1.1. Case 1 – dense and continuous catalytic metal layer .............................................................................. 46 3.1.2. Case 2 – porous and discontinuous catalytic metal layer .......................................................................... 48 3.1.3. Case 3 – sensing mechanism at temperatures above 700 ◦ C ....................................................................... 48 3.2. The selection of metal electrode ............................................................................................................. 49 3.3. The selection of dielectric layer .............................................................................................................. 49 3.4. Existing SiC-based MOS capacitor hydrogen sensor ......................................................................................... 50 4. Future challenges .................................................................................................................................... 51 5. Conclusion ............................................................................................................................................ 52 Acknowledgements .................................................................................................................................. 52 References ........................................................................................................................................... 52 Biographies .......................................................................................................................................... 54 ∗ Corresponding author at: School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, Seri Ampangan, 14300 Nibong Tebal, Pulau Pinang, Malaysia. Tel.: +60 4 599 5259/+6 012 515 3540; fax: +60 4 594 1011. E-mail address: cheong@eng.usm.my (K.Y. Cheong). 0925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2010.09.059