Biomedical subjects

Hagen Schmidt

Publications and source records attributed to Hagen Schmidt.

3 recordsLinked to original sources

PubMed2005

Investigation of high power effects on Ti/Al and Ta-Si-N/Cu/Ta-Si-N electrodes for SAW devices.

Damage behavior of two different metallization systems (Ti/Al bilayer and Ta-Si-N/Cu/Ta-Si-N multilayer) as finger electrodes in surface acoustic waves (SAW) devices was investigated. A special test structure was developed for this reason. The samples were loaded with traveling SAWs varying input power and loading time. Simultaneously during these experiments, the electric behavior of the SAW structure was measured and damage development by voids and hillock formation was observed using optical microscopy, too. The damaged structures were investigated by means of different microscopy techniques. Results show that the Cu-based metallization system has a significantly higher acoustomigration resistance and power durability in comparison with the Al thin film system.

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PubMed2004

New SPUDT cell structures.

The present paper describes single-phase unidirectional transducers (SPUDT) cells with all fingers wider than lambda/8 while maintaining the unidirectional effect. The first solution is related to a SPUDT consisting of lambda/4 and lambda/2 wide fingers arranged in two tracks. Each track has no significant unidirectional effect. Both tracks form a waveguide, and the waveguide coupling generates the interaction of the tracks. As a result of that interaction, a unidirectional effect arises as verified by experiment. This transducer type is called double-track (DT) SPUDT. A second solution is suggested that includes, in contrast to distributed acoustic reflection transducer (DART), electrode width control (EWC), and Hunsinger cells, SPUDT cell fingers with one and the same width only. Cell types with lambda/6, lambda/5, and lambda/3 wide fingers called uniform width electrode (UWE) cells are considered. One of these cell types, including exclusively lambda/5 wide fingers, is experimentally investigated and a unidirectional effect is found. Moreover, a filter example using the lambda/5 cell type has been designed for reducing SPUDT reflections. The echo suppression expected could be verified experimentally. No waveguide coupling is required for this cell type.

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PubMed2003

The highly sensitive optical measurement of absolute SAW amplitudes for power flow analysis.

The established optical method for the measurement of surface acoustic wave (SAW) amplitudes (simple probing) has been modified to result in the effective separation of scattered light from the SAW-diffracted light by means of two single mode optical fibers. In this way, the photodetector noise is drastically reduced, and absolute SAW amplitudes of 10(-12) m can be detected easily. Using an additional precise measurement of the nondiffracted light by means of fiber shifting, the SAW amplitudes can be calibrated with an error of less than 3%. This method can be applied to deliver an accurate power flow analysis in SAW devices. As an example, for a YZ-LiNbO3 transducer, the measured and calculated SAW power densities were found to agree within better than 6%.

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