Research into esoteric microtechnologies that bridge the divide between humans and machines will be in evidence in December at the International Electron Devices Meeting (IEDM). Among the developments that will be presented in Washington are advances in display technologies, sensors and microelectromechanical-system design, including some for medical use.
Researchers at the University of Tokyo have fabricated a flexible, shock-resistant, lightweight Braille sheet display on a plastic film by integrating a plastic sheet actuator array with high-quality organic FETs in an active matrix. They claim it is the first demonstration to integrate plastic actuators with organic active matrices. The researchers predict the scheme will enable pocket-sized Braille e-books.
The array of rectangular plastic actuators is processed from a perfluorinated polymer electrolyte membrane. A small semisphere that projects upward from the rubberlike display surface is attached to the tip of each rectangular actuator. The effective display size is 4 x 4 cm. Each character consists of a 3 x 2 array of Braille dots, and the total number of dots is 144. Thus, 24 characters (six characters x four lines) can be displayed at a time.
The display's pentacene FETs, with top-contact geometry, have a channel length of 20 micrometers and a mobility of 1 cm2/Vs (volts x seconds). The Braille dots on one line are driven for 0.9 second. The total thickness of the device is 1 mm and the weight, 5.3 grams.
Researchers at Princeton University's electrical-engineering department will present the first ICs fabricated directly on a soft, elastic silicone substrate. In an all-dry fabrication process, amorphous-silicon transistors are prepared on rigid SiNx subcircuit islands and are interconnected with stretchable metallization.
Such work envisions fully flexible circuits that could stretch and relax reversibly, enabling applications ranging from prosthetic skin to sensor arrays that could be stretched over arbitrary surfaces.
The first cochlear electrode array to incorporate a full electronic position-measurement system will be reported by researchers at the NSF Engineering Research Center for Wireless Integrated MicroSystems at the University of Michigan. The group's work builds on its earlier results with a passive cochlear substrate process.
Bypasses defective cells
According to the researchers, nearly 100,000 people worldwide have received cochlear implants, in which a bundle of 16 to 22 wire electrodes is inserted into the cochlea. The wires electrically stimulate receptors in the auditory nerve, bypassing defective hair cells. Ideally, the implant should avoid damaging any surviving hair cells during insertion and should hug the inner ear's bony central support structure, called the modiolus, to minimize the distance to the receptors. The Michigan team's passive-substrate design achieved a modiolus-hugging rest shape.
The team's thin-film electrode array is fabricated using a conventional bulk-silicon-micromachining process. The silicon substrate is defined by a 3-micron boron etch-stop diffusion and is released using ethylene-diamine-pyrocatechol. Stress-relieved oxide-nitride dielectrics support aluminum interconnects to iridium oxide and polysilicon strain gauges. The present arrays are 12 mm long, sized for testing in a guinea pig.
The interface IC was designed and fabricated in a 0.5-micron AMI Semiconductor process. The 2.4 x 2.4-mm chip does data entry, data validation, sensor selection, and signal amplification and filtering.
MEMS to go
Researchers at Carnegie Mellon University (Pittsburgh) are evaluating mixer-filters made by micromachining composite metal and dielectric interconnect layers after the CMOS process is completed. In contrast to a front-end filter architecture, the intermodulation frequency to which the mixer-filter downconverts can be set below 1 GHz, letting the MEMS structures be made larger and with higher gain.
The research is leading toward resonant mixer-filters with 0-dB insertion loss and submilliwatt power in foundry CMOS MEMS technology, the team said. In the next generation, small subarrays will be linked to form channel-select filters.
Researchers at Sony Corp. are working on an embedded MEMS filter chip for VHF applications. While surface-acoustic-wave filters are widely used as bandpass filters, further reductions in SAW filter size are limited by the devices' physical properties. The Sony team used phosphorus-doped polysilicon film to fabricate the MEMS structure. The film was deposited as in situ phosphorus-doped amorphous silicon and then annealed for crystallization. The researchers fixed the beam's thickness to less than 1 micron, because it is hard to handle thicker films through conventional silicon processes. The other parameters were optimized during the mechanical simulation and experiments.
Toshiba Corp. researchers have developed a piezoelectric RF MEMS tunable capacitor using a CMOS-compatible surface-micromachining process. For the first time, they will report, a continuous wide tuning ratio of 3 has been realized at lower than 3-V operation.
Dalsa Professional Imaging (Eindhoven, Netherlands) has built a 28-Mpixel CCD image sensor with a 2 x 2 on-chip RGB charge-binning concept for high-end digital still cameras. The optical format is 44 x 33 mm with a pixel size of 7.2 micron2. The device contains a four-phase image section and three-phase bidirectional horizontal register.