Research Papers

A Study on Long-Term In Vitro Reliability of Intracochlear Lead-Zirconate-Titanate Microactuators

[+] Author and Article Information
Yifeng Liu

Department of Mechanical Engineering,
University of Washington,
3900 E Stevens Way NE,
Seattle, WA 98105
e-mail: louisliu@uw.edu

Chuan Luo

Department of Precision Instruments,
Tsinghua University,
30 Shuangqing Rd,
Haidian, Beijing 100084, China
e-mail: luochuan@gmail.com

G. Z. Cao

Department of Materials Science,
University of Washington,
302 Roberts Hall,
Seattle, WA 98195
e-mail: gzcao@uw.edu

Clifford R. Hume

Virginia Merrill Bloedel Hearing Research Center,
Department of Otolaryngology-Head
and Neck Surgery,
University of Washington,
VA Puget Sound, 1959 NE Pacific St,
Seattle, WA 98195
e-mail: hume@uw.edu

I. Y. Shen

Department of Mechanical Engineering,
University of Washington,
3900 E Stevens Way NE,
Seattle, WA 98105
e-mail: ishen@uw.edu

1Corresponding author.

Manuscript received March 11, 2018; final manuscript received April 27, 2018; published online May 28, 2018. Assoc. Editor: Xiaoning Jiang.

ASME J of Medical Diagnostics 1(3), 031005 (May 28, 2018) (8 pages) Paper No: JESMDT-18-1017; doi: 10.1115/1.4040103 History: Received March 11, 2018; Revised April 27, 2018

An intracochlear lead-zirconate-titanate (PZT) microactuator integrated with a cochlear implant electrode array could be a feasible strategy to implement combined electric and acoustic stimulation inside the cochlea. The purpose of this paper is to characterize in vitro a prototype PZT microactuator for intracochlear applications, including service life, failure mechanisms, and lead leaching. PZT microactuators were driven sinusoidally to failure in air and in artificial perilymph. Frequency response functions (FRFs) and electrical impedance were monitored. After the PZT microactuators failed, the amount of leached lead was measured via inductive coupled plasma mass spectrometry (ICP-MS). Two failure mechanisms are identified: electrical breakdown and structural failure. The electrical breakdown, possibly from loss of parylene encapsulation, is evidenced by a sudden and significant drop of the actuators' electrical resistance. The structural failure, possibly from electrode delamination, is evidenced by a sudden and significant drop of FRFs. The amount of lead leached from the PZT microactuator is well below published safety guidelines from federal agencies.

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Fig. 1

An intracochlear PZT microactuator: (a) hybrid implant in cochlea, (b) cross section of the actuator, and (c) prototype actuator probe

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Fig. 2

The sample and experimental setups: (a) sealed environment for long-term reliability tests and (b) experimental setup for frequency response measurements

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Fig. 3

The electrical model for the actuator probe: (a) the electrical model for impedance curve fitting and (b) typical impedance curve fitting for actuator in air

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Fig. 4

The mechanical behavior of the actuator during the reliability test in air: (a) time history of FRF magnitude and (b) typical FRF measurement

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Fig. 5

The static gain curve over time for a PZT actuator probe soaked in the artificial perilymph without driving

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Fig. 6

Resistance stages: the parallel resistance Rp and correction exponent α over time for the PZT thin film under inner or outer electrode while soaking in the artificial perilymph

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Fig. 7

Comparison of impedance magnitude and extracted resistance Rp of the actuator in stage-2 of the soaking test and the bare actuator dwelled in perilymph: (a) the impedance magnitude and (b) the extracted resistance Rp of the bare actuator

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Fig. 8

The static gain at 10 kHz over time for PZT actuator probes driven in the artificial perilymph environment

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Fig. 9

The parallel resistance (Rp) of the diaphragm driven in the artificial perilymph by inner or outer electrode over time

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Fig. 10

Schematic views of the actuator diaphragm: (a) stage-1: well protected and insulated, (b) stage-2: electrical failure, (c) stage-3: mechanical failure, and (d) thick parylene coating that seals PZT pores



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