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ZnO Etching and Microtunnel Fabrication for High-Reliability MEMS Acoustic Sensor

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This paper describes a technique for uniform step coverage of aluminum metal (Al) on ZnO film in the fabrication of MEMS acoustic sensor. The MEMS acoustic sensors were fabricated by etching ZnO layer in three different etchants: HCl, NH4Cl with electrolytically added copper ions, and NH4OH with electrolytically added copper ions. For the first time, a technique is reported, which uses aqueous NH4OH solution with electrolytically added copper ions for etching of ZnO layer. For reliable operation of the device, the electrical testing of Al step coverage on ZnO layer was performed. The maximum currents
that can be drawn across Al-deposited ZnO edge etched by HCl, Cu-added NH4Cl, and Cu-added NH4OH were 40 mA, 2.5 A, and 3.0 A respectively, without any damage to the structures. The investigations show that uniform Al step coverage on ZnO layer is obtained in case of NH4OH with electrolytically added
copper ions. During fabrication of the device, a novel technique for building a microtunnel for pressure compensation was also developed. This microtunnel is used to compensate the pressure applied on the silicon diaphragm by connecting the cavity to the atmosphere. To realize the smooth inlet of microtunnel in the cavity, photoresist SU8 was used for patterning the cavity after microtunnel etching. The developed technique for microtunnel fabrication reduces the process complexity, providing improved yield of the device. The packaged device performed satisfactorily in the sound pressure level (SPL) of 120–160 dB over a wide frequency range of 30–8000 Hz. The maximum sensitivity of the sensor was measured
as 380 μV/Pa.
Index Terms—Electrolytic copper addition, ZnO film, bulk micromachining, Si-diaphragm, TMAH.

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Informasi Detail

Judul Seri

IEEE TRANSACTIONS ON DEVICE AND MATERIALS RELIABILITY

No. Panggil

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Penerbit

New York : IEEE., 2014

Deskripsi Fisik

IEEE TRANSACTIONS ON DEVICE AND MATERIALS RELIABILITY, VOL. 14, NO. 1, MARCH 2014

Bahasa

English

ISBN/ISSN

1530-4388

Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

VOL. 14, NO. 1, MARCH 2014

Subjek

TEKNIK

Info Detail Spesifik

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Pernyataan Tanggungjawab

Yuli/Agus

Versi lain/terkait

Lampiran Berkas

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