Kurt O. Wessendorf

Resonator/Oscillator response to liquid loading.

The resonant frequency of a thickness-shear mode resonator operated in contact with a fluid was measured with a network analyzer and with an oscillator circuit. The network analyzer measures changes in the devices intrinsic resonant frequency, which varies linearly with (ρη)(1/2), where ρ and η are liquid density and viscosity, respectively. The resonator/oscillator combination, however, responds differently to liquid loading than the resonator alone. By applying the operating constraints of the oscillator to an equivalent-circuit model for the liquid-loaded resonator, the response of the resonator/oscillator pair can be determined. By properly tuning the resonator/oscillator pair, the dynamic range of the response can be extended and made more linear, closely tracking the response of the resonator alone. This allows the system to measure higher viscosity and higher density liquids with greater accuracy.

Micromachined conformal electrode array for retinal prosthesis application

Retinal prosthesis projects around the world have been pursuing a functional replacement system for those with retinal degeneration. In this paper, we will outline the concept for a micromachined conformal electrode array and present preliminary fabrication results. Individual electrodes are designed to float on micromachined springs on a substrate that will enable the adjustment of spring constants and therefore contact force by adjusting the dimensions of the springs at each electrode. This will also allow us to accommodate the varying curvature/topography of the retina. We believe that this approach will provide several advantages by improving the electrode/tissue interface as well as generating some new options for in-situ measurements and overall system design.

Retinal implant electrode arrays with 10V SOI CMOS circuitry

The interface between stimulation electrodes (which deliver electrical pulses) and retinal tissue is the most important interface in the retinal prosthesis application. As a member of the DOE Artificial Retina project, we have been developing a micromachined electrode array to address the critical mechanical and electrical coupling at this interface. Our design incorporates mechanical springs at each electrode site to allow controlled mechanical contact between the electrode array and the retinal surface, as well as built-in 10V capable CMOS electronics to handle routing of signals and to monitor integrated sensors. This process is also directed towards addressing other MEMS sensor/actuator systems that require higher voltages (/spl sim/10V).

MEMS conformal electrode array for retinal implant

Retinal prosthesis projects around the world have been pursuing a functional replacement system for patients with retinal degeneration. In this paper, the concept for a micromachined conformal electrode array is outlined. Individual electrodes are designed to float on micromachined springs on a substrate that will enable the adjustment of spring constants-and therefore contact force-by adjusting the dimensions of the springs at each electrode. This also allows the accommodation of the varying curvature/topography of the retina. We believe that this approach provides several advantages by improving the electrode/tissue interface as well as generating some new options for in-situ measurements and overall system design.

Post-Processed Integrated Microsystems

This report represents the completion of a three-year Laboratory-Directed Research and Development (LDRD) program to develop a low cost platform for integrated microsystems that is easily configured to meet a wide variety of specific applications-driven needs. Once developed, this platform, which incorporates many of the elements that are common to numerous microsystems, will enable integrated microsystem users access to this technology without paying the high up-front development costs that are now required. The process starts with the fabrication, or acquisition, of wafers which have sparsely placed device or circuit components fabricated in any foundried technology (Si CMOS or bipolar technologies, high-frequency GaAs technologies, MEMS, etc.). We call these “smart substrates.” Using the diverse processing capabilities of SNL, we then intend to “post-process” high-value components in open areas on the front or back of the wafers and microelectronically integrate the added components with the pre-placed circuitry. Examples of post-processed components include sensors, antennas, SAW devices, passive elements, micro-optics, and surface-mounted hybrids. The combination of preplaced electronics and post-processed components will enable the development of many new types of integrated microsystems. Targeted applications include integrated sensor systems, tags, and electromechanical systems.