This paper presents a study on micro package technology using conformal coating of parylene C as non hermetic packaging material for implantable biomedical devices. Different thicknesses (2-25 μm) of parylene C were coated on patterned two electrode PCB test board for electrical performance measurement. Experiments were carried out in 85°C salient solutions for accelerated testing. Test results on survive life will be presented, which serves as a baseline for minimum coating thickness of implantable biomedical devices. Water vapor transmissions (WVT) through parylene C thin films combined with additional oxide/nitride coatings to form multilayer vapor barrier films were also evaluated. Test results show that multilayered coating approach has improved the WVT rate by a factor of 54.7%, compared with a single parylene C coating during 24 hours test period.

This paper reports the micro-power telemetry unit that can sense pressure, humidity, and bio-potentials, for the study of micro-package techniques for implantable biomedical micro-systems used in research, diagnosis and therapy. The micro-package study is aimed to develop and demonstrate the micro-package technology for micro-implants to have an implant life of 0.2 to 2.0 years. The telemetry device consumes <; 1.0 μA at 3 volts, with a volume <; 0.2 cm3 including lithium rechargeable battery, and has RF links to charge Li battery and to receive external on-off commands. The device output pulse width changes with a capacitive pressure sensor; and the pulse period changes with an external resistor as the humidity sensor or the bio-potential signals in series with the resistor. The first model of telemetry units, packaged with silicon and epoxy only, lasted more than 70 days in 40°C saline solution. The RF recharging and on-off control circuits was tested, and the lifetime of second generation telemetry unit are being evaluated.

This paper presents research results on novel high performance silicon piezoresistive strain sensors based on Smart-Cut (TM) SOI wafer, with 340 nm silicon overlayer and 1 mu m buried oxide. Experimental results show that the 3 k Omega Wheatstone bridged piezoresistive strain sensor has a sensitivity of 0.14 mV/mu epsilon at 5V bias and a linearity of 0.9 % full scale, in the range of +/- 1000 mu epsilon. When tested at elevated temperatures, the gage factor of the sensor changed from 27.6 at 24 degrees C to 25.4 at 130 degrees C, equivalent to a temperature coefficient of the gauge factor of -0.02 /degrees C, which is an order of magnitude smaller than the -0.55 /degrees C value of previous sensors developed with 2x10(18) cm(-3) doping. This piezoresistive sensor is suitable for applications that need high temperature stability.

Package is a critical part in biomedical implantable systems. Many factors affecting the host body and the life time of implantable systems need to be considered. Package becomes more critical for microfabricated systems with wireless charging and communication. This paper presents the first phase study on micro package techniques for short term (30 to 90 days) implantable systems. A MEMS implantable telemetry model system was designed for packaging evaluation. The transmitter was custom designed and fabricated using MOSIS processes and an external receiver was designed and built for data collection. For short term implantable systems, medical grade silicone outer coating is used for ldquotissue compatibilityrdquo; while multilayer polymeric and nanometer-thin metal or ceramic films were used for inner coatings to provide mechanical strength and to block vapor and moisture penetration. The total coating thickness is less than 0.6 mm. The electrical performances (leakage resistance) of test board and model devices coated with various package materials and processes are evaluated in 40degC saline. This paper presents: the model system; the evaluation methods and analysis of failure modes of polymeric coating on test boards; the solution to the failures and suggested coating techniques of polymeric materials; and the evaluation of model systems packaged with multi-layer coatings in 40degC saline. The expected performance of developed packaging method was verified by experiments. Implantable wireless MEMS system can be packaged with thin multilayer materials to have an expected life time greater than 30 days.

This paper describes the design of a functional strain sensing module with large dynamic range (80dB), DC to 10kHz response, high resolution, and mini size for industrial applications, such as the rolling-element bearings research. The design of the MEMS capacitive strain sensor employs mechanical amplifications of package design and buckle beams as well as the linear differential comb capacitor. The sensor is interfaced with a low noise charge amplifier, mixer, and filter circuits to provide an analog output that demonstrated a resolution of 0.09 microstrains with a maximum range of ±1000 microstrains. The sensor and the electronic circuits, including a temperature sensor, can be integrated on a chip, and packaged as a small functional unit. Additional electronics were integrated with the interface circuit on the chip that provide A/D conversion, radio frequency power supply, and digital signal telemetry to a near-by control unit. Preliminary test results are compared with the design simulation.

This paper reports on a novel, bonding-free method to fabricate silicon carbide-on-insulator (SiCOI) substrates. The process bypasses wafer bonding by using a high deposition rate polysilicon process in conjunction with wet chemical etching to produce wafer-thick polysilicon layers that serve as substrates for the SiCOI structures. Because wafer bonding is not used, insulators of various material types and thickness can be used. Using this method, transfer percentages over 99% are readily achievable. Various applications could benefit from this technology, including high temperature SiC-based microelectromechanical systems (MEMS) and SiC electronic devices.