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A new low power integrated pressure sensor system with digital output (1 bit PDM signal) for medical applications is presented. The absolute pressure sensor comprising 400 nm thick surface micromachined polysilicon membranes for capacitive pressure detection and a monolithic integrated 2nd order sigma–delta-modulator including voltage reference and timing generator is extremely miniaturized on an area of approximately 3 mm 2 . For protection and biocompatibility reasons the sensor is coated with a silicone elastomer of up to 100 μm thickness, which does not influence the sensor's performance. The sensor system was tested in vitro in physiological NaCl solution, showing excellent results compared to a commercial available reference sensor. The sensor system is working well down to a supply voltage of 2.2 V with a power consumption of 0.5 mW. The resolution is better than 12 bit. Due to the small chip area, low power consumption and cost effective production process, the sensor is ideal for medical applications, e.g., in combination with telemetric power and data transmission [J. Zacheja, B. Clasbrummel, J. Binder, U. Steinau, Implantable Telemetric Endosystem for Minimal Invasive Pressure Measurements, MedTech95, Berlin, Germany, (1995)] as an implantable sensor to reduce the mortality risk of intensive care patients.

We report a novel process for the full integration of surface-micromachined pressure-sensor cells into a standard BiCMOS process. Only the standard layers of the BiCMOS process are used to build up the sensor and only one additional photolithography step is necessary to achieve the micromachined structures. The application of the process is demonstrated by means of an integrated pressure-sensor system at a working range of 0.1 to 1.1 bar of absolute pressure. The influence of process parameters and tolerances of the VLSI process on the sensor performance are examined. To examine the long-term stability, the sensors are electrically deflected at the resonance frequency applying 4 × 10 11 load cycles. The measurements do not show any changes in the mechanical behaviour, so a very high long-term stability can be proven. In contrast to all integrated micromechanical systems presented so far, neither prenor post-processing of the system is necessary. Compared to conventional surface micromachining, the additional processing effort for the sensor realization is reduced dramatically to about 5% of the BiCMOS process.

Results on a new approach for the monolithic integration of micromechanics and electronics are presented. The same process steps and layers can be used for both the mechanical and the electronic elements. This is a promising process concept for integrated microelectromechanical systems with a minimum of additional costs compared to the standard electronics process. Results on the fabrication of micromechanical structures using the process steps of a 0.8 μm CMOS process are given. The sublimation technique is used to dry the released surface-micromachined structures and different sublimating chemicals are compared. The influences of polycrystalline and amorphous deposition as well as diffusion doping and ion implantation on the strain gradients of the structural layers are presented. A fabricated electrostatically deflectable and capacitively detectable cantilever is presented and the dependence of the capacitance on the drive voltage is shown. By using the presented theory and fitting calculations to the measured non-linear characteristic, a value of 170 GPa for Young's modulus of the polysilicon film is extracted.

The paper presents a new technology for electrostatically driven ultrasound transducers, processed by only a few additional steps within a standard BiCMOS process. Measurements of the test structures showed good acoustic properties especially for application in fluids. The full integration with the electronic circuit allows the realization of a new generation of one- and two dimensional arrays for many different applications like low cost phased arrays or 2D arrays for specific medical applications like skin diagnosis.

A pure CMOS integrated accelerometer was realised using surface micromachining as structural technique. The samples were fabricated by a 14 mask 0.8 /spl mu/m CMOS standard process in a Siemens production line. Only the standard layers of the process (350 nm polysilicon and 600 nm oxide as sacrificial layer) are used to build up the surface micromachined device. Sensor release and antisticking are also CMOS-compatible. The movement of a seismic mass normal to the chip surface is capacitively detected (open loop) and transformed on chip into a digital output signal by a robust circuit for measuring sub-fF capacitance differences. Parasitics are suppressed on chip. The sensor was designed to measure accelerations up to 50 g. A resolution of /spl plusmn/0.6 g corresponding to a capacitance change of /spl plusmn/0.1 fF was observed.

A new low power integrated pressure sensor system with digital output (1 bit PDM signal) for medical applications is presented. The absolute pressure sensor comprising 400 nm thick surface micromachined polysilicon membranes for capacitive pressure detection and a monolithic integrated 2/sup nd/ order sigma-delta-modulator including voltage reference and timing generator is extremely miniaturized on an area of approximately 3 mm/sup 2/. For protection and biocompatibility reasons the sensor is coated with a silicone elastomer of up to 100 /spl mu/m thickness, which does not influence the sensor's performance. The sensor system was tested in vitro in physiological NaCl solution, showing excellent results compared to a commercially available reference sensor. The sensor system is working well down to a supply voltage of 2.2 V at a power consumption of 0.5 mW. The resolution is better than 12 bit. Due to the small chip area, low power consumption and cost effective production process, the sensor is ideal for medical applications, e.g. in combination with telemetric power and data transmission as an implantable sensor to reduce the mortality risk of intensive care patients.

The knowledge of the cavity pressure and the tightness of sealed surface micromachined membranes is essential for the description of their behavior and for the evaluation of their long-term stability. We are presenting a novel procedure to determine the cavity pressure and the tightness of sealed surface micromachined structures. The basic idea for cavity pressure determination is to compare two pressure-dependent resonance frequency measurements of a sealed and subsequently opened structure. The pressure dependent resonance frequency of the sealed structure depends on the clamping conditions, while the resonance frequency of the opened structure strongly depends on the compression of the gas-film between the plates. To characterize the structures with high accuracy a setup containing a temperature and pressure controlled chamber was installed. To equalize the ambient and the cavity pressure after the first characterization the sealed structures have to be opened by means of with an focused ion beam (FIB) and again measured pressure-dependent. An important application of the developed method is on-wafer process monitoring of surface micromachining processes.