A multichannel adaptive integrated MEMS/CMOS microphone
Lead Research Organisation:
University of Edinburgh
Department Name: Integrated Micro and Nano Systems
Abstract
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Publications
Al-Masha'al A
(2017)
Fabrication and characterisation of suspended microstructures of tantalum
in Journal of Micromechanics and Microengineering
Al-Masha'al A
(2016)
Evaluation of residual stress in sputtered tantalum thin-film
in Applied Surface Science
Koickal T
(2009)
A programmable spike-timing based circuit block for reconfigurable neuromorphic computing
in Neurocomputing
Latif R
(2016)
MEMS design and modelling based on resonant gate transistor for cochlear biomimetical application
in Microsystem Technologies
Latif R
(2010)
Microelectromechanical systems for biomimetical applications
in Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena
Latif R
(2011)
Low frequency tantalum electromechanical systems for biomimetical applications
in Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena
Mastropaolo E
(2012)
Bimaterial electromechanical systems for a biomimetical acoustic sensor
in Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena
Mastropaolo E
(2013)
Control of stress in tantalum thin films for the fabrication of 3D MEMS structures
in Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena
Rebecca Cheung (Author)
(2010)
MEMS Systems for Biomimetrical Applications
| Description | The key findings are: 1. During the development of MEMS-RGT arrays, the bridge gates have been designed to cover the audible frequency range signals of 20Hz - 20kHz. Aluminium and tantalum have been studied as the material for the bridge gate structure. The downstream etch release technique employing oxygen/nitrogen plasma has been developed to release the bridge gate structure from a sacrificial layer. In the first iteration, aluminium bridge gates have been fabricated. The presence of tensile stress within aluminium had caused the aluminium bridge gates of length >1mm to collapse. In order to address this issue, tantalum bridge gates have been fabricated in the second iteration. Straight tantalum bridge gates in tensile stress and buckled tantalum bridge gates in compressive stress have been characterised. The frequency range of 550Hz - 29.4kHz has been achieved from the fabricated tantalum bridge gates of length 0.57mm - 5.8mm. 2. The channel and source/drain regions have been fabricated and integrated with the aluminium or tantalum bridge gate structures to create the MEMS-RGTs. In this study, the n-channel and p-channel resonant gate transistor (n-RGT and p-RGT) have been considered. The p-RGTs have been found to possess considerably less substhreshold currents than n-RGTs. The threshold voltage, transconductance and substhreshold current for both n-channel and p-channel resonant gate transistor devices have been characterised, where the channel conductance of the n-RGT and p-RGT devices has been modulated successfully and the tuning capability within the audible frequency range has been achieved from the tantalum bridge gates of the p-RGT devices. The characterisation and optimisation of the resonant gate transistor provide the first step towards the development of the adaptive RGT cochlear biomodel for the neuromorphic auditory system application. 3. A spike event coded MEMS-RGT microphone model for neuromorphic auditory systems has been developed. Our microphone system directly converts acoustic signal into bandpassed filtered outputs and encode them as asynchronous spike time events. The microphone system alters its dynamic response by receiving inputs in the spike domain which are then decoded to vary the gate voltage of the MEMS-RGT. The MEMS-RGT sensor model has been simulated and the measurement results from the spike encoder chip for a simulated MEMS-RGT response have been achieved. A set of 10 MEMS-RGT sensors using an etch release process capable of releasing long resonant gate transistor bridges from the sacrificial layer have been fabricated (see point 2). 4. An analogue low-noise MEMS interface circuit which has very small parasitic capacitance at the input node has been designed and fabricated. The circuit is suitable for the MEMS cochlea-mimicking acoustic sensors which are highly parasitic-sensitive due to their low intrinsic sensing capacitance. In order to reduce the electronic noise of the interface circuit, chopper stabilization technique is implemented, and an effective method to optimize the critical transistor size for best noise performance is derived. Simulation results show that, for a MEMS sensing structure with 200 fF static capacitance, the interface circuit achieves a 0.72 aF equivalent capacitance noise floor over 100 Hz to 20 kHz audio bandwidth. Results from fabricated devices have verified simulation results in the test laboratory and a journal paper presenting the scheme with results is under review for publication in IEEE Transactions on Biomedical Circuits and Systems. 5. An analogue cochlea-mimicking filter has been modelled, designed and fabricated in analogue VLSI. The circuit design uses floating active inductors in high-Q and steep cut-off elliptic filters to achieve a response comparable with the biological exemplar. Our implementation offers the advantages of tuning with one variable parameter, high-Q and a steep cut-off response, providing an overall performance that closely matches the biological exemplar. Results from fabricated devices have verified simulation results and have been published in the journal IEEE Transactions on Biomedical Circuits and Systems. 6. A simulated form of the output of the microphone (which codes the signals from multiple sensors) has been used in an experiment to test the effectiveness of the data so coded in differentiating different types of musical instruments. This experiment was carried out to assess the effeciveness of the proposed coding technique when applied to real sounds. |
| Exploitation Route | Our findings can be taken forward by optimising our design and processing further, for example, by employing more robust materials and improved design concepts. |
| Sectors | Healthcare |
| URL | http://mems.cs.stir.ac.uk/ |