Ren Tianling

Design optimization of beam-like ferroelectrics-silicon microphone and microspeaker

Design optimization of beam-like ferroelectrics-silicon integrated microphone and microspeaker is studied. The Pt/Pb(Zr,Ti)O3/Pt/SiO2/Si3N4 cantilever structure is designed theoretically using multimorph model. The sensitivity and the sound pressure level (SPL) of the integrated microphone and microspeaker are calculated. It is found that the sensitivity of the microphone and the SPL of the microspeaker are very high. This integrated microphone and microspeaker will be valuable for high quality micro-acoustic devices.

Characterization of Mn-Doped Ba1-xSrxTiO3 Thin Films Prepared by the Sol-Gel Method

Undoped and Mn-doped Ba1-xSrxTiO3 (BST) thin films have been fabricated on Pt/Ti/SiO2/Si by an aqueous acetate sol-gel method. The BST stock solution can be easily mixed with an aqueous metal ion solution and is stable at room temperature. The annealing temperature of the doped and undoped films is between 650-750°C. The x-ray photoelectron spectra results show that the Mn 2p3/2 valence state in the BST is the same as that of the original Mn(II) dopant. The dielectric constant of the BST thin films can be increased to 800, and the loss tangent can be decreased to 0.01 due to the Mn(II) doping. The leakage current of the BST films can also be greatly reduced.

Micro packaged MEMS pressure sensor for intracranial pressure measurement

This paper presents a micro packaged MEMS pressure sensor for intracranial pressure measurement which belongs to BioMEMS. It can be used in lumbar puncture surgery to measure intracranial pressure. Miniaturization is key for lumbar puncture surgery because the sensor must be small enough to allow it be placed in the reagent chamber of the lumbar puncture needle. The size of the sensor is decided by the size of the sensor chip and package. Our sensor chip is based on silicon piezoresistive effect and the size is 400 × 400 μm2. It is much smaller than the reported polymer intracranial pressure sensors such as liquid crystal polymer sensors. In terms of package, the traditional dual in-line package obviously could not match the size need, the minimal size of recently reported MEMS-based intracranial pressure sensors after packaging is 10 × 10 mm2. In this work, we are the first to introduce a quad flat no-lead package as the package form of piezoresistive intracranial pressure sensors, the whole size of the sensor is minimized to only 3 × 3 mm2. Considering the liquid measurement environment, the sensor is gummed and waterproof performance is tested; the sensitivity of the sensor is 0.9 × 10−2 mV/kPa.

Simulation and design of micro pressure sensors applied to measure the intracranial pressure

This paper reports a micrometer level pressure sensor to measure the intracranial pressure (ICP). The sensor is based on the piezoresistive effect. The piezoresistive pressure sensor is simulated and designed by using nonlinear programming Optimizing and Finite Element Analysis (FEA) tools. The sensor is fabricated by MEMS process. From tests, the sensor samples performances match up the design.

Impedance Spectroscopy Analysis of Cell-Electrode Interface

Many chronically implanted electrodes suffer sensitivity loss in their applications in brain computer interface systems. It is hard to diagnose the cause of the problem because few measures are available to analyze directly what happened on the cell-electrode interface. In this paper, the impedance characterization of the cell-electrode interface was discussed in detail using equivalent circuit approach, which was used to evaluate the cause of the electrode sensitivity loss. The impedance spectroscopy of the cell-electrode interface acts as a function of several parameters, such as the sealing resistance and the shunt capacitance between the microelectrode and the electrolyte. Changes of the impedance spectroscopy can be traced to the parameter changes of the equivalent circuit, which reflect the status of the cell-electrode interface, such as the cell-electrode gap change, the erosion of microelectrodes, and so on. The circuit impedance simulation results give an important reference for the monitor of the cell-electrode connection, and are also helpful for the improvement of the microelectrode design

A Novel Fabrication Method for Flexible SOI Substrate Based on Trench Refilling with Polydimethylsiloxane

Flexible arrays based on the flexible connection of double layers are demonstrated. Flexible sensor arrays are highly desired for many applications. Conventional flexible electronics are implemented by directly fabricating them on organic flexible substrates such as polyimide or polyethylene terephthalate, or forming on rigid substrates and then transferring them onto elastomeric substrates. For the first time, a novel process method based on trench refilling with polydimethylsiloxane to make flexible arrays is proposed. In this method, the sensors are directly fabricated on islands of the final bulk silicon. The performance of the sensor will not to be effected by bending and stretching operations. A one-dimensional flexible array shows good flexibility. Since the flexibility process is the last fabrication step, this method is compatible with many micro-electro-mechanical system fabrication technologies and has good yield.

Low Power and High Sensitivity MOSFET-Based Pressure Sensor

Based on the metal-oxide-semiconductor field effect transistor (MOSFET) stress sensitive phenomenon, a low power MOSFET pressure sensor is proposed. Compared with the traditional piezoresistive pressure sensor, the present pressure sensor displays high performances on sensitivity and power consumption. The sensitivity of the MOSFET sensor is raised by 87%, meanwhile the power consumption is decreased by 20%.

Influences of Interface States on Resistive Switching Properties of TiOx with Different Electrodes

Different TiOx thin films prepared by graded or sufficient oxidization of Ti are applied with Pt or Ag electrode in metal-insulator-metal (MIM) structures for studying the properties and mechanisms of resistive switching. The differences on the mobile oxygen vacancies in TiOx films and different work functions of the electrode films result in different insulator-metal interface states, which are displayed as ohmic-like or non-ohmic contact. Based on the interface states, the electrical models for MIM devices are analyzed and extracted. The electrode-limited effect and the bulk-limited effect can be unified to explain the mechanisms for resistive switching behavior as the dominant effect respectively in various conditions. All the current-voltage curves of the four kinds of specimens measured in the experiments can be explained and proved in accordance with the theory.

MEMS PIEZOELECTRIC ACOUSTIC TRANSDUCER

ABSTRACT This paper presents the fabrication process and measurement results of microelectro-mechanical (MEMS) piezoelectric acoustic transducers. To increase the output sound pressure, a dome-shaped multi-layer diaphragm is designed and fabricated by adjusting the residual stress in the individual layers. Transducers work in either audio or ultrasonic frequency range if diaphragm is designed in different size. In the frequency range from 100 Hz to 7 kHz, the output sound pressure of audio transducers with 3 mm × 3 mm diaphragm is higher than 0.1 Pa. The maximum output reaches 1.1 Pa at 3.8 kHz. For ultrasonic transducers with 1 mm × 1 mm diaphragm, the maximum output is 1.26 Pa at resonant frequency of 54 kHz. All transducers show acceptable linearity over a wide range of input drive voltage.

Wafer-Scale Flexible Surface Acoustic Wave Devices Based on an AlN/Si Structure *

Wafer-scale flexible surface acoustic wave (SAW) devices based on AlN/silicon structure are demonstrated. The final fabricated devices with a 50μm-thickness silicon wafer exhibit good flexibility with a bending curvature radius of 8 mm. Measurements under free and bending conditions are carried out, showing that the central frequency shifts little as the curvature changes. SAW devices with central frequency about 191.9MHz and Q-factor up to 600 are obtained. The flexible technology proposed is directly applied to the wafer silicon substrate in the last step, providing the potential of high performance flexible wafer-scale devices by direct integration with mature CMOS and MEMS technology.