Clemens Krüger

Development of a Completely Encapsulated Intraocular Pressure Sensor

A completely encapsulated intraocular pressure (IOP) sensor equipped with telemetric signal and energy transfer is introduced integrated into a silicone disc for implantation into the eye. After implantation into enucleated pig eyes and into rabbit eyes in vivo, the IOP was recorded and compared to established techniques of IOP measurement. Pressure chamber tests showed that the sensor functioned correctly after biocompatible encapsulation in polydimethylsiloxane. In vivo and in vitro tests in rabbit and pig eyes demonstrated that the implanted system worked with the same precision as established techniques for IOP determination. The correlation between the measurements with the implanted device and pneumotonometry in several experiments was between 0.9 and 0.99. This device serves as a functioning model for the realization of a telemetric IOP sensor for integration into an artificial intraocular lens. Such a device will open new perspectives, not only in the management of glaucoma, but also in basic research for mechanisms of glaucoma.

Initial investigations on systems for measuring intraocular pressure

Basic investigations on an intraocular implant system for continuous measurements of the intraocular pressure (IOP) are introduced. The system consists of a pressure sensor connected to transponder components integrated in the haptic of an artificial soft intraocular lens. External transponder components will be integrated in a spectacle and a hand-held unit. The influence of the lens material on the pressure sensor performance will be discussed in detail. Two pre-version of the concept mentioned will be introduced. In the first version, a pressure sensor was connected to a microwire. In a second version, the sensor was connected to transponder components for wireless data and energy transmission. Both versions were encapsulated in standard soft intraocular lens material. Pressure measurements show the same sensitivity before and after encapsulation. In addition, a small offset was observed due to the influence of the silicone coating. The performances of the sensors have the same precision as widely accepted gold standard for the determination of the IOP.

Micro-springs for temporary chip connections

The idea of Composite IC is an assembly concept for multi-chip assembly that allows to detect and exchange defective components before final mounting and encapsulation. This paper describes the fabrication process and the characterization of a scalable micro-spring design that has the potential of meeting the mechanical requirements of the Composite IC concept. An FEM simulation model capable of predicting the mechanical properties of future design variations is shown.

Platform for Temporary Testing of Hybrid Microsystems at High Frequencies

In this paper, a platform based on the composite-IC concept that is optimized for high-frequency (HF) applications will be presented. Surface-micromachined microsprings are used for temporary connection and testing. This provides the system with an individual compensation of different contact heights due to production tolerances. In addition, self-alignment structures have been added to compensate lateral tolerances. The presented self-alignment structures were designed to compensate rising precision requirements in contrary to commonly used placing machines. Key elements of the HF platform are coplanar waveguides and microsprings that are processed using microelectromechanical-system technologies on alumina ceramic. Microsprings with outer dimensions between 2000 and 125 mum with different beamwidths, beam thicknesses, and beam lengths were designed, simulated, and fabricated. All structures were tested mechanically and electrically. As a further development, spiral microsprings are presented. These combine minimal space requirement with no preferred orientation. Positioning in an individual array is possible. Due to the design and the integration of the spiral microsprings as part of the flip-chip connection, the scattering parameters show excellent HF performance up to frequencies of 9 GHz. The same microsprings could also be used for onboard testing on multichip modules (MCMs). This provides the MCM with cheap and powerful testability and reworkability. This paper covers the mechanical and electrical design, simulation, optimization, production, and characterization of suitable microsprings.

TRANSPONDER SYSTEM FOR NON-INVASIVE MEASURMENT OF INTRAVASCULAR PRESSURE

Monitoring of blood pressure and pulse rate offers diagnostical and therapeutical opportunities in hypertension disease and arrhythmia, respectively. This paper presents an intravascular pressure monitoring system consisting of an implantable silicone capsule, which can be placed in an arterial system via a catheter. The capsule contains a pressure sensor and signal conditioning circuits for wireless data and energy transfer using 6.78 MHz transponder technology.

Fabrication and Characterization of a PZT thin Film Actuator for a Micro Electromechanical Switch Application

Micromachined silicon cantilever beams actuated by the converse piezoelectric effect are of great interest for actuator applications, e.g. micro relays or micro mirrors. For the miniaturization and cost saving aspects the combination of silicon bulk micromachining and chemical solution deposition (CSD) technique for the ceramic thin films is very promising. This paper presents the results of such a fabrication process for a PbZr 0.45 Ti 0.55 O 3 (PZT) thin film micro actuator for a switch application. The actuator was designed with lengths of 190-990 μm, widths of 60-120 μm, and a complete thickness of 1.5 μm. Wherein the piezoelectric PZT function layer has a thickness of 350 nm. For a distance of 10 μm between the switch contacts and an applied voltage of 10 V a finite element analysis simulation (FEA) was carried out to obtain the principal stress contribution, the optimum cantilever length, the sensitivity, the resonance frequency and the switch contact force. The bending beams were characterized by laser interferometry, resonance frequency, and force measurements. These characterization results are compared to the FEM analyses and to an analytical approach.