Sören Hirsch

Ceramic injection molded clevis sensor for online substance concentration measurement

The current research presents recent respective to the work development of a ceramic clevis sensor for online substance concentration measurements. The aim is to develop a robust and acid-resistant sensor device, which can be easily included in existing procedural pipeline systems. To achieve those goals a lot of factors had to be checked. For the substance concentration measurements a capacitive sensor effect has been chosen. With this method even low substance concentrations down to one-tenth of a per cent can be indentified.

Microelectromechanical structures in langasite (La/sub 3/Ga/sub 5/SiO/sub 14/) by wet chemical etching

Lanthanum gallium silicate (langasite, La/sub 3/Ga/sub 5/SiO/sub 14/) is a new piezoelectric material with promising properties for micro-electromechanical applications at high temperatures. So far it has been used for SAW and BAW devices. This paper reports on the possibility of fabricating microstructures in langasite by wet chemical etching. The etching behavior of different chemicals applying different mask materials was investigated. Further, the effect of doping on the etching behavior was studied. As a first demonstrator a cantilever beam in langasite has been produced showing the possibility of MEMS in langasite. The resonance spectrum of this device was recorded at temperatures up to 600/spl deg/C.

Gas detecting langasite membranes by wet chemical etching

Piezoelectrically actuated membranes in lanthanum gallium silicate (langasite) were fabricated. The membranes have shown operating temperatures up to 850 degC and are applied as high temperature gas detecting devices by means of CeO2 sensor films. The measurements show, that gas sensing with membranes is feasible and results in even higher frequency shifts as for thick plan-parallel resonators. A multi-step wet chemical etching process has been developed and was used to structure the langasite. Furthermore, membranes have been fabricated by using the different etch characteristics of doped and undoped langasite

Development of a mechanical stress-analysing-tool to characterize packaging processes

This paper reports on the development of a measurement system to detect mechanical stress caused by packaging processes. A piezoresistiv silicon test chip is used to convert the inducted mechanical stress into a resistance change, measured by a developed resistance analyser. The sensor interface is capable to measure a high number of resistors with a high measurement rate. Thus, also rapid proceeding packaging processes can be characterized. Furthermore, the developed software calculates the stress distribution along the whole die, which includes a compensation of the systematic errors e.g. the temperature dependence of the piezoresistive coefficients.

Multitouch touchless — A new approach with optical proximity sensing

This paper introduces a new approach to detect multiple inputs for touchless human machine interfaces. It is based on optical proximity sensing with visible or infrared light. It is described the principle of modulation, demodulation and system design. In the last part, some applications are presented to use this approach. The approach is based on multiple modulated light sources. The modulation is a form of direct sequence spread spectrum technique. One main advantage of the design is, that only one receiver is needed to detect multiple inputs. This held the system cost low.

Microwave Emission of Carbon Fibres during Electrical Breakdown

A new method of reliability monitoring of electrical devices based on carbon fibres is presented. Due to the thermo-mechanical stress on electronic circuits a loss of fibre network integrity can take place and potential difference may appear between the edges of broken carbon fibres. This potential difference causes an intensive field-emission from surfaces of these broken carbon fibres and an acceleration of emitted electrons. Due to the acceleration of electrons a microwave emission is generated. A CFRP was used to simulate the behaviour of a carbon based electronic device. The sequence of microwave impulses was detected in a frequency bandwidth from 8 to 12 GHz. The rise time of detected microwave impulses is about of few nanoseconds. This time is in agreement with crack formation time in carbon fibre. The correlation between the change of electrical resistance of composites and microwave impulses by fibres fracture is observed. Thus, the breakdown of current that flows through carbon fibres induces detectable microwave emission. That means that defects in electrical circuits can be wireless detected online.

An in situ measurement system for the mechanical impact of the PCB processing chain on stress sensitive devices

In the past, silicon based measurement system were used to characterize packaging induced stresses of electronic devices [1]. In this paper a new approach for qualifying mechanical PCB manufacturing processes is presented. Silicon based package equivalents (S3MD; Stress Sensitive Surface Mounted Devices) are used instead of real devices at locations of expected dangerous mechanical impact. The silicon based package equivalents have strain sensitive structures implemented. These structures are formed by thin film processes and are designed as strain sensitive metal resistors. Therefore, the mechanical impact of the following steps in the PCB process chain can be monitored. The sensor devices are qualified in the AEC Q200 “board flex” test to get the limiting strain values. In the result, we show a new method to get in situ measured data of the mechanical impact of PCB manufacturing processes.

Toolbox for detection of mechanical and thermo-mechanical stress in electronic components

This paper reports the development process of a measurement system for mechanical stress detection. A piezoresistive silicon sensor chip is used to convert the inducted mechanical stress into a resistance change, measured by a developed resistance analyzer. Aim of our work was to simplify the sensor chip for high flexibility in design and adaption. The sensor chip can easily adapt to a device under test and can be conditioned to perform long-term, in-situ measurements of mechanical stress in electronic components and packages. Therefore all sensor intelligence packed in the resistance meter unit. This is controlled by a specialized software program. To increase the measuring accuracy all resistors measured by the Four-Point-Method with modified routing layout. Given that, up to 96 resistive signals can be measured. Though the modular design, the whole system gains high flexibility in respect of the application field.