Ernst Obermeier

Microactuators and their technologies

Abstract This paper gives a brief overview of microactuators, focussing on devices made by microfabrication technologies which are based on silicon processes like photolithography, etching, thin film deposition etc. These technologies enable the miniaturization of electrical devices as well as micromechanisms and microactuators. They can be batch fabricated on large area silicon substrates and represent the smallest available in a vast field of actuators. Mentioning the activation principles and the three main fabrication technologies: bulk micromachining, surface macromachining and moulding, the paper focusses on devices, which made their way into industrial applications or prototypes. The far most developed micro electro-mechanical systems (MEMS) are found in micro-fluidic systems (printheads, microvalves and -pumps) and micro-optical systems (micromirrors, -scanners, -shutters and -switches). They can be combined with microelectronics and microsensors to form an integrated on-chip or hybrid-assembled system. Other MEMS-actuators like microgrippers, microrelays, AFM heads or data storage devices, are promising devices for future medical, biological and technical applications like minimal invasive surgery or the vast field of information storage and distribution.

Polysilicon as a material for microsensor applications

Abstract Important characteristics of boron-doped LPCVD polysilicon layers with regard to sensor applications are presented. Properties such as the resistivity, temperature coefficient of the resistance, gauge factor and long-term stability are described. A pressure sensor utilizing polysilicon piezoresistors with a measurement range of 1 bar and a sensitivity of roughly 11 mV/V FS, a laser-trimmed polysilicon temperature sensor with a sensitivity of −3.4 × 10 −3 K −1 and non-linearity of less than 0.5% and a pressure sensor with polysilicon-based on-chip calibration and temperature compensation are described.

Piezoresistive pressure sensors based on polycrystalline silicon

Abstract Polycrystalline Si (poly-Si) has found various applications in microelectronics and micromechanical devices such as pressure sensors, accelerometers and actuators. Poly-Si films deposited on an oxidized Si substrate can combine the excellent mechanical properties of Si with the efficient electrical insulation of poly-Si piezoresistors, so that improved stability and high-temperature operation can be obtained. Different poly-Si fabrication techniques are reviewed with emphasis on their applications to pressure sensors. The theoretical interpretation and models of the piezoresistivity in poly-Si and experimental results are presented. The calculation of the longitudinal and transverse gauge factors and their correlation with the crystallographic structure of the poly-Si film are discussed. The possibility of sensor performance optimization including mechanical, temperature and piezoresistive properties of a device is demonstrated. Two examples of commercially manufactured poly-Si sensors and an example of a new poly-Si technology are also presented.

Sputtered molybdenum oxide thin films for NH3 detection

Abstract Thin films of MoO3 for gas sensing applications have been deposited by reactive sputtering using a metallic molybdenum target. After annealing at 500°C in air, the layers consist of rhombic molybdenum trioxide with a (010) texture. The morphology of the layers considerably depends on the film thickness. Electrical conductivity measurements with different test gases show that MoO3 layers are suitable for NH3 detection at operating temperatures between 400 and 450°C.

Combustion gas sensitivity of zeolite layers on thin-film capacitors

Abstract Y-zeolites doped with platinum by an ion-exchange process have been used as gas-sensitive layer material on thin-film interdigital capacitors (IDCs). The zeolite-IDC sensor sensitivity has been determined for C 4 H 10 , CO and H 2 in wet air by exciting the sensor with an alternating voltage and determining the impedance response.

Micro gas-flow sensor with integrated heat sink and flow guide

Abstract A microsensor for gas-flow sensing applications with high sensitivity (700 mV at a flow velocity of 2.7 m s −1 and a supply voltage of 3 V), low power consumption (8 mW at 55 K over-temperature and an airflow velocity of 0.8 m s −1 ) and short response time is presented. A heat sink and flow guide integrated on the backside of the microsensor is used to modulate the temperature distribution on the diaphragm to achieve an extended measurement range. Results from device simulation, technological processing and sensor performance are discussed.

A high temperature pressure sensor with /spl beta/-SiC piezoresistors on SOI substrates

This paper reports about the first piezoresistive pressure sensor for high operating temperatures using single crystalline, n-type /spl beta/-SiC piezoresistors on Silicon On Insulator (SOI) substrates. The new Silicon Carbide On Insulator (SiCOI) layer structure prevents a leakage current flow through the substrate at high temperatures up to 723 K. The sensor was tested in the temperature range between room temperature and 573 K. The sensitivity of the device at room temperature is approximately 20.2 /spl mu/V/VkPa. This corresponds to a longitudinal gauge factor of -32 in the [100]-direction. The Temperature Coefficient of Sensitivity (TCS) is -0.16 %K/sup -1/ at 573 K.

A micromachined single-chip inkjet printhead

Abstract A new smart single-chip microsystem inkjet printhead, called the ‘Backshooter’, is presented in this paper. It combines micromechanics including heating actuators, temperature sensor, channels and nozzles with a smart CMOS circuit including signal processing along with bidirectional data transfer and 60 V power amplifiers in a single silicon chip. Prototypes with 50 nozzles and a system pitch down to 42 μm (appropriate for 600 dpi print resolution) will be demonstrated. The Backshooter microsystem technology makes it possible to reduce the chip dimensions to 22 mm 2 (at 50 nozzles and 300 dpi), less than half of a standard layout. It enables a lower market price and a much better printhead functionality to be achieved.

High temperature piezoresistive β-SiC-on-SOI pressure sensor with on chip SiC thermistor

Abstract This paper reports about a piezoresistive β-SiC-on-silicon on insulator (SOI) pressure sensor with an on chip polycrystalline SiC thermistor for high operating temperatures. The β-SiC film was characterized by TEM-analysis, X-ray diffraction and Hall measurements. The investigations show a good single crystal quality of the β-SiC film and a reliable electrical isolation by the buried oxide layer from the substrate at temperatures up to 673 K. The fabricated pressure sensor chip was tested in the temperature range between room temperature and 573 K. The sensitivity at room temperature is S =2.0 mV V −1 bar −1 . The temperature coefficient of the sensitivity (TCS) between room temperature and 573 K is TCS=−0.16 %K −1 . The temperature coefficient of the resistivity (TCR) of the polycrystalline SiC thermistor is TCR=−0.17 %K −1 .

Heat-conduction microsensor based on silicon technology for the analysis of two- and three-component gas mixtures

Abstract A sensor for measuring the thermal conductivity of gases is presented, which is suitable for the analysis of binary and ternary gas mixtures. The principles of thermal conductivity measurement is distinguished by the lack of hysteresis, short response times, continuous measurement, low drift and lack of wear and tear. The dimensions of the sensor chip are 3.5 mm × 3.5 mm × 0.25 mm. The sensor has a power consumption of 13 mW and a thermal time constant of 7.3 ms at 100 K over-temperature, with N2 as the test gas. This paper deals with the manufacture of the sensor, the methods of describing its behaviour by simulation and the test procedures for its characterization.