Edvard Kaelvesten

3D micromachined devices based on polyimide joint technology

A novel and simple technology for making robust 3D silicon structures with small radii of bending has been developed and investigated. The proposed self-assembling method of bending 3D structure out-of-plane, without the use of interlocking braces is based on thermal shrinkage of polyimide in V-grooves. The static bending angle for the permanent out-of-plane rotated structure can be chosen and well controlled over a wide range by varying the curing temperature of the polyimide and the number of V-grooves in the joint.

New concept for CMOS-compatible fabrication of uncooled infrared focal plane arrays using wafer-scale device transfer bonding

In this paper we present a new membrane transfer bonding technology for fabrication of uncooled infrared focal plane arrays (IRFPAs). The technology consists only of low temperature processes, thus, it is compatible with standard integrated circuits (ICs). In the future this technology may allow infrared detectors with high temperature annealed, high performance thermistor materials to be integrated in CMOS based uncooled IRFPAs. The infrared detectors and the ICs are processed and optimized on different wafers. The wafer with the detectors (sacrificial detector-wafer) is bonded to the IC wafer (target wafer) using low temperature adhesive bonding. The detector-wafer is sacrificially removed by etching or by a combination of grinding and etching, while the detectors remain on the target wafer. The detectors are mechanically and electrically contacted to the target wafer. Finally, the adhesive bonding material is sacrificially removed. One of the unique advantages of this technology is the ability to integrate small, high temperature annealed detectors and ICs. We have applied membrane transfer bonding to the fabrication of arrays of infrared bolometers with polycrystalline silicon thermistors. In principle, membrane transfer bonding can be applied to the fabrication of any type of free-standing transducer including bolometers, ferroelectric detectors and movable micro-mirrors.

Optical MEMS at Silex Microsystems

Silex Microsystems produces Silicon Optical Benches and Silicon Optical Mirrors for a variety of customers on an international market. The core of the activity is the MEMS chip itself and the related processes. By qualifying processes Silex provides the opportunity for clients to increase the degree of development in the MEMS cores of their products. The designs are customized in order to meet the specifications for a wide customer base with even wider demands. The Silicon Optical Benches can incorporate BCB layers in order to integrate RF-lines and make it possible to design for example coils of high performance. The polysilicon resistors have been qualified to be stable within 3-ppm over 6 months at elevated temperatures. The polysilicon temperature dependence makes it possible to use the resistors in order to measure temperature and excludes thermistors from the designs. Electrical feed through vias can be incorporated to enable backside connection and simplify packaging. The Silicon Optical Mirrors are produced both as large arrays of small mirrors and smaller arrays of larger mirrors depending on applications. Also for the mirrors the incorporations of electrical vias simplify design and process issues. The pads under the mirrors are connected from backside and it is possible to avoid difficult contacting down in cavities.

Teaching sensor technology and MEMS processing using an in-house educational MPW process

This paper presents a new innovative way of teaching modern sensor technology and practical MEMS-processing by using an in-house Multi Project Wafer (MPW) process especially developed for education purposes. This process has been used as the base for a project course called Sensor Technology, which includes a substantial laboratory component. In this project, the student actively follows the complete sensor development process from design and fabrication to the evaluation of modern MEMS sensors. The design and CAD work for five different sensor types (each having several different versions) has completed prior to the course but the students are introduced to the tools used for the design and simulation of microstructures. The students themselves perform most of the fabrication steps in the cleanroom and all evaluation of the fabricated sensors. Our new in-house MPW-process allows the students to fabricate five different piezoresistive sensor types for measuring flow (both mechanical and thermal transducers), acceleration (both 1- and 3-axis), pressure and angular velocity using one mask set consisting of only four masks. Each sensor type then is produced in many different versions (size and geometry) giving the students flexibility to choose sensors for specific applications during the sensor evaluation. Successful evaluations of pressure, flow and acceleration sensors fabricated by the students have been carried out. The sensor evaluation part also gives the student experience in practical electrical measurements on real devices. Both the course concept and the unique educational MPW-process will be described in this paper.