Henrik Rödjegård

Capacitive slanted-beam three-axis accelerometer: I. Modelling and design

Three-axis accelerometers based on four separate seismic masses, each one suspended on a slanted beam, have previously been shown to have identical resolution and frequency responses in all directions. Here, a new and in-depth model of such accelerometers is presented. The theoretical model incorporates non-ideal effects such as the finite aspect ratio of the beam and the frequency-dependent squeezed gas-film damping. Sensitivity, resolution, transverse sensitivity and process errors are discussed. Prototype devices have been fabricated in a straightforward silicon process.

A PCB-like process for vertically configured thermopiles

Thermopiles are important components in infrared thermal detectors, thermoelectric generators and thermoelectric coolers. We present a thermopile structure with up to 224 vertically arranged thermocouple legs in a polyimide flex material. The thermopile is optimized for infrared thermal radiation detection and is fabricated using printed circuit board-like (PCB-like) processing. Each thermoelectric leg consists of a bundle of a few hundred sub-micrometre-sized strands of either antimony or nickel. These metal wire bundles were achieved by employing ion track technology on the polyimide foil, resulting in a porous dielectric material. Electrochemical methods were used to grow the thermoelectric materials in the pores. The plating mask was produced in a laminated dry photoresist. A small metal cross section, 20 µm2 (1 vol%), ensured a low heat exchange between the two surfaces of the flex. The typical resistance per thermocouple was 34 Ω. A responsivity to irradiance of 4.3 V mm2 W−1 was measured when heating with a white light source (irradiance 1 mW mm−2).

MICRO PINBALL GAME DEMONSTRATING AN EASY MEMS TRANSFER PROCESS USING ROOM TEMPERATURE PLASMA BONDING

An easy wafer level transfer process for fabrication of electrostatically actuated structures such as bulk micromachined motors or cantilevers is described. The actual structures were fabricated by dry etching of a donor wafer, transferred to a handling wafer using room temperature oxygen plasma assisted bonding and then revealed through etchback of the donor wafer. Notching during the dry etch was avoided since there is no need for a buried oxide etch stop layer. Etch depth differences after the dry etch were eliminated in the etchback step. The process was used to fabricate MEMS demonstrators in the form of micro pinball games and microelectromechanical wobble motors. This process is a low cost alternative to using SOI wafers and it also circumvents some of the problems of deep dry etching that arise when using buried etch stop layers as in the case of SOI wafers. Another advantage of using SOI wafers is that double-sided micromachining becomes less complicated.

Capacitive slanted-beam three-axis accelerometer: II. Characterization

Three-axis accelerometers based on four separate seismic masses, each one suspended on a slanted beam, have previously been theoretically shown to have identical resolution and frequency responses in all directions. New simulation and models for this type of accelerometers have been developed and these are verified with measurements of the g-vector, shaker measurements and optical modal analysis. The measurements show good agreement with the new models. The results also show that the slanted-beam topology is a promising alternative for future three-axis accelerometer designs.

An easy-to-implement method for evaluation of capacitive resonant sensors

A novel method that can be used to characterize resonant capacitive sensors is presented. The method is based on measurement of the third harmonic of the current through the capacitor; thus the detection signal is frequency separated from the excitation signal. The measurement is time-continuous and only requires a very simple resonant structure where a single electrode is simultaneously used for excitation and detection. The readout circuit is easily implemented with a single operational amplifier and standard equipment such as a lock-in amplifier or a function generator and a spectrum analyzer. Measurements of a resonant structure confirm the feasibility of the concept.

A Monolithic Three-Axis Accelerometer with Symmetric Properties

A monolithic three-axis accelerometer has been designed and manufactured. The design is based on SOI material to minimize the chip area and to include over-range protection and squeezed gas film damping. The accelerometer consists of four single axis accelerometers with their respective sensitive axes in different (111) directions. This type of accelerometer senses x-, y-, and z-axis accelerations with identical resolution. Models that predict the sensitivity and frequency behaviour have been developed and verified in measurements.

Replication of continuous-profiled micro-optical elements for silicon integration

A novel scheme for the integration of diffractive optical elements onto silicon is presented. The processing is made in reverse order, meaning that the process of structuring the optical elements on the wafer precedes the silicon microstructuring. The first processing step on the wafer is the hot embossing of the optical microstructures into an amorphous fluorocarbon polymer spin coated on the wafer. The cured polymer forms a highly stable material with excellent optical properties. The remaining silicon processing is thus performed with the diffractive optical elements already in place. Two different diffractive structures were used in the development of the method-a (Fresnel) lens with a rather low f-number and a diffractive element producing a fan-out of a large number of paraxial beams.

Fabrication of an infrared emitter using a generic integration platform based on wire bonding

This paper reports a novel approach for the fabrication of infrared (IR) emitters for non-dispersive IR gas sensing. The proposed concept enables the integration of superior resistive heater materials with microelectromechanical system structures. In this study, non-bondable filaments made of nickel chromium are attached to mechanical attachment structures using a fully automated state-of-the-art wire bonder. Formation of electrical contact between the integrated filaments and the electrical contact pattern on the substrate is performed using conventional gold stud bumping technology. The placement accuracy of the integrated filaments is evaluated using white-light interferometry, while the contact formation using stud bumping to embed the filaments is investigated using focused ion beam milled cross-sections. A proof-of-concept IR emitter has been successfully operated and heated up to in continuous mode for 3 h.

Bulk micromachining of SOI wafers using double sided lithography and anisotropic wet etching

A novel method of manufacturing bulk micromachined components in SOI material with anisotropic wet etching is presented. The SOI material reduces the total chip size compared to standard bulk micromachining since the slopes are shorter. It also adds functionality to the components, such as inherent overload protection and squeezed air-film damping. The method is based on double sided lithography and anisotropic wet etch of the thin device layer of the SOI wafer. The lithography on the back of the buried oxide is carried out either by electro deposition of the photoresist PEPR 2400 or by spraying ma-P 215S. A highly symmetric three-axis accelerometer has successfully been manufactured in a 50 micrometers thick SOI film.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Flexible PCB Vertical Thermopile IR Sensor

We present the design, fabrication and characterization of vertical thermopile infra-red (IR) sensors. The sensors are produced in batches in a standard flexible printed circuit board (flex PCB) material. The vertical design opens up for large area detection and longer thermopile chains. The sensors consist of series of 88 vertically interconnected thermocouples in a 75 mum thick polyimide foil (Kapton HNtrade). The sensors showed a voltage response to an IR pulse of 1.2 V/(W/mm2).