Malaysian Journal of Analytical Sciences Vol 23 No 2 (2019): 345 - 354

LASER-ASSISTED SILICON ETCHING FOR MICRO FUEL CELL ELECTRODE PLATE FABRICATION

(Fabrikasi Plat Elektrod Sel Bahan Api Mikro dengan Punaran Silikon Terbantu Laser)

Umi Azmah Hasran¹*, Siti Kartom Kamarudin^1,3, Burhanuddin Yeop Majlis², Wan Ramli Wan Daud³, Abdul Amir Hassan Kadhum³, Gandi Sugandi⁴

¹Fuel Cell Institute

²Institute of Microengineering and Nanoelectronics

³Department of Chemical and Process Engineering

Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia

⁴Research Center for Electronics and Telecommunication

Lembaga Ilmu Pengetahuan Indonesia, Bandung, Indonesia

*Corresponding author: umi.h@ukm.edu.my

Received: 13 April 2017; Accepted: 17 April 2018

Abstract

Silicon electrode plates for micro fuel cells were obtained using a microfabrication process based on the micro-electro-mechanical system (MEMS) technology. The dry etching process involved the laser ablation technique using the highly stable Nd:YAG. This technique is suitable for micromachining silicon substrates. The total size of the electrode plate was 2.5 cm x 2.5 cm and the active reaction area was 1 cm². An increase in laser scan numbers deepened the groove being etched on the silicon sample, but it showed a saturated behavior as the number of scans became higher. The time required to etch a complete electrode plate flow field with 14 square-shaped through-holes of 0.185 cm x 0.185 cm area using laser ablation was ~30 minutes, which was much shorter than the wet etching time of more than 10 hours with the potassium hydroxide solution (KOH) solution. The laser-etched flow field achieved vertical sidewalls as per the original design, whereas the wet-etched structure achieved a typical anisotropic hole structure with sidewalls that were approximately 54º to the electrode surface due to the <100> orientation of the silicon wafer. Therefore, the laser ablation technique was chosen to produce the electrode plates for the micro fuel cell as it can save time on the etching process and produce more precise flow field dimensions for the electrode plates with less process steps compared with the conventional wet etching processes using KOH solution.

Keywords: flow field design, MEMS technology, bulk micromachining, dry etching technique, laser ablation

Abstrak

Plat silikon untuk sel ahan api mikro dihasilkan menggunakan proses mikrofabrikasi yang berasaskan teknologi sistem mikro-elektro-mekanikal (MEMS) dengan proses punaran kering menggunakan teknik ablasi laser. Jenis laser yang digunakan untuk kerja punaran kering ini adalah Nd:YAG berkestabilan tinggi yang sesuai untuk pemesinan mikro bagi substrat silikon. Saiz keseluruhan plat elektrod yang dihasilkan adalah 2.5 cm x 2.5 cm, manakala kawasan aktif tindakbalas adalah 1 cm². Peningkatan bilangan imbasan menjadikan kawasan terablasi pada sampel lebih dalam tetapi punaran menjadi semakin tepu apabila bilangan imbasan semakin meningkat tinggi. Masa untuk memunar habis medan aliran plat elektrod yang mempunyai 14 lubang tembus berbentuk segi empat sama dengan keluasan 0.185 cm x 0.185 cm dengan menggunakan laser hanyalah kira-kira 30 minit, berbanding dengan proses punaran basah menggunakan kalium hidroksida (KOH) yang memakan masa lebih 10 jam. Proses yang lama ini juga memerlukan lapisan SiO₂ yang lebih tebal sebagai pelindung silikon semasa proses punaran dijalankan. Malah, punaran basah KOH ke atas wafer silikon dengan orientasi <100> memberi ciri lubang dengan dinding yang bersisi sendeng pada sudut ~ 54º dari permukaan plat dan mengakibatkan bukaan lubang mempunyai saiz yang lebih kecil daripada rekabentuk asal. Oleh itu, teknik ablasi laser dipilih untuk menghasilkan plat elektrod bagi mikro sel fuel kerana ia dapat menjimatkan masa mikrofabrikasi dan menghasilkan dimensi medan aliran untuk plat elektrod yang lebih tepat dengan langkah aliran proses mikrofabrikasi yang kurang berbanding dengan proses punaran basah menggunakan larutan KOH.

Kata kunci: rekabentuk medan aliran, teknologi MEMS, pemesinan mikro pukal, proses punaran kering, teknik ablasi laser

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