Rhonira Latif

Low frequency tantalum electromechanical systems for biomimetical applications

The integration of p-channel metal-oxide-semiconductor transistors and tantalum bridge structures for the fabrication of resonant gate transistors (RGTs) that operate in the audible frequency range has been developed. Resonant gate transistors with channel length of 15 μm and clamped-clamped tantalum bridges of 0.5 mm to 1.6 mm in length have been fabricated. The measured first modal frequency of the bridges has been found to be higher than the expected theoretical value. From the experimental and theoretical analysis of the first three modes, the stress in the bridges has been extracted and found to be tensile with values of 3 MPa – 10 MPa. Finite element simulation has validated the extracted stress and the mode shapes of the tantalum bridges. The modulation of conductance in the channel region between the source and drain by the tantalum bridge of the RGT has been demonstrated. The threshold voltage and transconductance of the fabricated p-channel RGT have been measured to be −37 V and 6.84 μS, respect...

Microelectromechanical systems for biomimetical applications

An etch release process capable of releasing long resonant gate transistor bridges from a sacrificial layer has been studied as a step towards developing a system to mimic the cochlear mechanism inside the human ear. The developed etch release process involves the use of a gentle etch tool that is capable of a clean and damage-free etch release. The influence of temperature and oxygen/nitrogen gas flow rates on the undercut etch rates and the profiles of photoresist and polyimide sacrificial layers have been investigated. An array of aluminum bridges of length 0.278–1.618 mm, which cover the frequencies from 1 to 33.86 kHz, has been designed and released from a sacrificial layer. The resonating beams have been measured.

Design of a spike event coded RGT microphone for neuromorphic auditory systems

This paper presents the design of a spike event coded resonant gate transistor microphone system for neuromorphic auditory applications. The microphone system employs an array of resonant gate transistors (RGT) to transduce acoustic input directly into bandpass filtered analog outputs. The bandpass filtered analog outputs are encoded as spike time events by a spike event coder and are then transmitted asynchronously by using the Address Event Representation (AER) protocol. The microphone system is designed to receive external inputs in the spike time domain to actively control the RGT response, a feature not present in other MEMS microphone systems implemented so far. System level simulations showing the response of the RGT sensor model and its spike event coded response are presented.

Bimaterial electromechanical systems for a biomimetical acoustic sensor

Bimaterial planarized micromechanical beams have been designed, simulated, and fabricated with lengths in the range 800–5800 μm and distance to substrate 0.8–4.0 μm. The beams are to be used as vertical-mode resonant gates on p-type field-effect transistors for implementing an adaptable MEMS acoustic sensor inspired by the human ear. A process for fabricating planar bilayer double-clamped beams made of silicon nitride (SiN) and aluminum (Al(1%Si)) has been developed. The planar design and bimaterial approach allow the fabrication of relatively straight beams with length up to 5800 μm with the possibility of controlling the degree of static deflection of the beams. The fabricated beams have shown a maximum deflection of ∼300 nm and a transverse concave shape with respect to the substrate due to the bilayer nature of the structure. From wafer curvature measurements, the stress in the SiN and Al(1%Si) is 200 and 280 MPa, respectively. Finite element simulations and analysis of the profile of the beams have d...

A low-noise interface circuit for MEMS cochlea-mimicking acoustic sensors

This paper proposes a low-noise MEMS interface circuit which has very small parasitic capacitance at the input node. The circuit presented 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.

Platinum and Aluminium Microresonator Bridges for Artificial Basilar Membrane

The artificial basilar membrane has been developed to mimic the mechanical performance of the basilar membrane in the cochlea. The artificial basilar membrane consists of an array of microbridgeresonators that are mechanically sensitive to the perceived audible frequency range between 20 Hz to 20 kHz. In this work, the finite element (FE) model of the microbridge resonators have been designed in Comsol Multiphysics 4.3 to work close to the audible frequency range. The lumped element (LE) model of the microbridge resonators have been calculated and compared to the simulated FE model. The microbridge resonators array with 0.5 μm thickness, 20 μm width and length varying from 275 μm up to 7700 μm have been designed using two different materials, i.e., platinum (Pt) and aluminium (Al). The microbridge resonators have been found to mimic closely the tonotopicorganisation characteristics of the basilar membrane. From the FE and LE models of the Pt and Almicrobridge resonators, Pt has been found to be a better material than Alfor the artificial basilar membrane design. For the same geometrical dimensions, the Ptmicrobridge resonatorsoperate within the audible frequency range while the Almicrobridge resonatorsoperate approximately 43%-53% above the audible frequency range.

Surface Modification of Electroosmotic Silicon Microchannel Using Thermal Dry Oxidation

A simple fabrication method for the surface modification of an electroosmotic silicon microchannel using thermal dry oxidation is presented. The surface modification is done by coating the silicon surface with a silicon dioxide (SiO2) layer using a thermal oxidation process. The process aims not only to improve the surface quality of the channel to be suitable for electroosmotic fluid transport but also to reduce the channel width using a simple technique. Initially, the parallel microchannel array with dimensions of 0.5 mm length and a width ranging from 1.8 µm to 2 µm are created using plasma etching on the 2 cm × 2 cm silicon substrate <100>. The oxidation of the silicon channel in a thermal chamber is then conducted to create the SiO2 layer. The layer properties and the quality of the surface are analyzed using scanning electron microscopy (SEM) and a surface profiler, respectively. The results show that the maximum oxidation growth rate occurs in the first 4 h of oxidation time and the rate decreases over time as the oxide layer becomes thicker. It is also found that the surface roughness is reduced with the increase of the process temperature and the oxide thickness. The scallop effect on the vertical wall due to the plasma etching process also improved with the presence of the oxide layer. After oxidation, the channel width is reduced by ~40%. The demonstrated method is suggested for the fabrication of a uniform channel cross section with high aspect ratio in sub-micro and nanometer scale that will be useful for the electroosmotic (EO) ion manipulation of the biomedical fluid sample.

Straight Bridge Beams with Centered Diaphragm (SBBCD) design for MEMS cochlear biomodel

This paper presents the development of an artificial basilar membrane (ABM) in order to biologically mimic the performance of a cochlea in human auditory system. The developed ABM should operate in an audible frequency range of a normal human ear which is in between 20 Hz to 20000 Hz. Two microelectromechanical system (MEMS) cochlear biomodel design; Straight Bridge Beams (SBB) and Straight Bridge Beams with Centered Diaphragm (SBBCD), have been considered for ABM development. Comsol Multiphysics software is used to design ABM and simulate their performance in terms of resonant frequency and static capacitance. SBB MEMS cochlear biomodel was designed with the dimension of 0.5 μm thickness, 20 μm width and in a range of 275 μm to 7700 μm length. As for SBBCD MEMS cochlear biomodel, an additional circular diaphragm with a diameter size of 75 μm is introduced to the center of the beam length. The SBBCD MEMS cochlear biomodel gave better performance with 2.84 % - 49.47 % of resonant frequency reduction and 9.44 % - 141.95 % of static capacitance increment in comparison with SBB MEMS cochlear biomodel.

Development of micro-electromechanical system (MEMS) cochlear biomodel

Human cochlear is undeniably one of the most amazing organs in human body. The functional mechanism is very unique in terms of its ability to convert the sound waves in the form of mechanical vibrations into the electrical nerve impulses. It is known that the normal human auditory system can perceive the audible frequency range between 20 Hz to 20 kHz. Scientists have conducted several researches trying to build the artificial basilar membrane in the human cochlea (cochlear biomodel). Micro-electromechanical system (MEMS) is one of the potential inventions that have the ability to mimic the active behavior of the basilar membrane. In this paper, an array of MEMS bridge beams that are mechanically sensitive to the perceived audible frequency has been proposed. An array of bridge bridge beams with 0.5 µm thickness and length varying from 200 µm to 2000 µm have been designed operate within the audible frequency range. In the bridge beams design, aluminium (Al), copper (Cu), tantalum (Ta) and platinum (Pt) ha...