Tayfun Akin

A wireless implantable multichannel digital neural recording system for a micromachined sieve electrode

This paper reports the development of an implantable, fully integrated, multichannel peripheral neural recording system, which is powered and controlled using an RF telemetry link. The system allows recording of /spl plusmn/500 /spl mu/V neural signals from axons regenerated through a micromachined silicon sieve electrode. These signals are amplified using on-chip 100 Hz to 3.1 kHz bandlimited amplifiers, multiplexed, and digitized with a low-power (<2 mW), moderate speed (8 /spl mu/s/b) current-mode 8-b analog-to-digital converter (ADC). The digitized signal is transmitted to the outside world using a passive RF telemetry link. The circuit is implemented using a bipolar CMOS process. The signal processing CMOS circuitry dissipates only 10 mW of power from a 5-V supply while operating at 2 MHz and consumes 4/spl times/4 mm/sup 2/ of area. The overall circuit including the RF interface circuitry contains over 5000 transistors, dissipates 90 mW of power, and consumes 4/spl times/6 mm/sup 2/ of area.

A single-crystal silicon symmetrical and decoupled MEMS gyroscope on an insulating substrate

This paper presents a single-crystal silicon symmetrical and decoupled (SYMDEC) gyroscope implemented using the dissolved wafer microelectromechanical systems (MEMS) process on an insulating substrate. The symmetric structure allows matched resonant frequencies for the drive and sense vibration modes for high-rate sensitivity and low temperature-dependent drift, while the decoupled drive and sense modes prevents unstable operation due to mechanical coupling, achieving low bias-drift. The 12-15-/spl mu/m-thick single-crystal silicon structural layer with an aspect ratio of about 10 using DRIE patterning provides a high sense capacitance of 130 fF, while the insulating substrate provides a low parasitic capacitance of only 20 fF. A capacitive interface circuit fabricated in a 0.8-/spl mu/m CMOS process and having a sensitivity of 33 mV/fF is hybrid connected to the gyroscope. Drive and sense mode resonance frequencies of the gyroscope are measured to be 40.65 and 41.25 kHz, respectively, and their measured variations with temperature are +18.28 Hz//spl deg/C and +18.32 Hz//spl deg/C, respectively, in -40/spl deg/C to +85/spl deg/C temperature range. Initial tests show a rate resolution around 0.56 deg/s with slightly mismatched modes, which reveal that the gyroscope can provide a rate resolution of 0.030 deg/s in 50-Hz bandwidth at atmospheric pressure and 0.017 deg/s in 50-Hz bandwidth at vacuum operation with matched modes.

A micromachined silicon sieve electrode for nerve regeneration applications

A micromachined silicon sieve electrode has been developed and fabricated to record from and stimulate axons/fibers of the peripheral nervous system by utilizing the nerve regeneration principle. The electrode consists of a 15-/spl mu/m-thick silicon support rim, a 4-/spl mu/m-thick diaphragm containing different size holes to allow nerve regeneration, thin-film iridium recording/stimulating sites, and an integrated silicon ribbon cable, all fabricated using boron etch-step and silicon micromachining techniques. The thin diaphragm is patterned using reactive ion etching to obtain different size holes with diameters as small as 1 /spl mu/m and center-center spacings as small as 10 /spl mu/m. The holes are surrounded by 100-200 /spl mu/m/sup 2/ anodized iridium oxide sites, which can be used for both recording and stimulation. These sites have impedances of less than 100 k/spl Omega/ @ 1 kHz and charge delivery capacities in the 4-6 mC/cm/sup 2/ range. The fabrication process is single-sided, has high yield, requires only five masks, and is compatible with integrated multilead silicon ribbon cables. The electrodes were implanted between the cut ends of peripheral taste fibers of rats (glossopharyngeal nerve), and axons functionally regenerated through holes, responding to chemical, mechanical, and thermal stimuli.<<ETX>>

Frequency Tunable Microstrip Patch Antenna Using RF MEMS Technology

A novel reconfigurable microstrip patch antenna is presented that is monolithically integrated with RF microelectromechanical systems (MEMS) capacitors for tuning the resonant frequency. Reconfigurability of the operating frequency of the microstrip patch antenna is achieved by loading it with a coplanar waveguide (CPW) stub on which variable MEMS capacitors are placed periodically. MEMS capacitors are implemented with surface micromachining technology, where a 1-mum thick aluminum structural layer is placed on a glass substrate with a capacitive gap of 1.5 mum. MEMS capacitors are electrostatically actuated with a low tuning voltage in the range of 0-11.9 V. The antenna resonant frequency can continuously be shifted from 16.05 GHz down to 15.75 GHz as the actuation voltage is increased from 0 to 11.9 V. These measurement results are in good agreement with the simulation results obtained with Ansoft HFSS. The radiation pattern is not affected from the bias voltage. This is the first monolithic frequency tunable microstrip patch antenna where a CPW stub loaded with MEMS capacitors is used as a variable load operating at low dc voltages

A low-cost uncooled infrared microbolometer detector in standard CMOS technology

This paper reports the development of a low-cost uncooled infrared microbolometer detector using a commercial 0.8 /spl mu/m CMOS process, where the CMOS n-well layer is used as the infrared sensitive material. The n-well is suspended by front-end bulk-micromachining of the fabricated CMOS dies using electrochemical etch-stop technique in TMAH. Since this approach does not require any lithography or infrared sensitive material deposition after CMOS fabrication, the detector cost is almost equal to the CMOS chip cost. The n-well has a TCR of 0.5-0.7%/K, relatively low compared to state-of-the-art microbolometer materials; however, it has negligible 1/f noise due to its single crystal structure. The use of polysilicon interconnects on the support arms instead of metal reduces the overall pixel TCR to 0.34%/K, but provides a better performance due to improved thermal isolation. Based on this pixel, a 16 /spl times/ 16 prototype focal plane array (FPA) with 80 /spl mu/m /spl times/ 80 /spl mu/m pixel size and 13% fill factor has been implemented, where built-in diodes are used to simplify array scanning, at the expense of reduced overall pixel TCR of 0.24%/K. The n-well microbolometer array with a simple readout scheme provides a responsivity of 2000 V/W, a detectivity of 2.6 /spl times/ 10/sup 8/ cmHz/sup 1/2//W, and an estimated NETD of 200 mK at 0.5 Hz frame rate. Considering that this performance can be further improved with low noise readout circuits, the CMOS n-well microbolometer is a cost-effective approach to implement very low-cost uncooled infrared detector arrays with reasonable performance.

A tunable multi-band metamaterial design using micro-split SRR structures

This paper presents the results of a feasibility study for the design of multi-band tunable metamaterials based on the use of micro-split SRR (MSSRR) structures. In this study, we have designed and constructed a conventional split-ring resonator (SRR) unit cell (type A) and two modified SRR unit cells having the same design parameters except that they contain two (type B) or four (type C) additional micro-splits on the outer square ring, along the arm having the main split. Transmission characteristics of the resulting MSSRR cells are obtained both numerically and experimentally and compared to those of the ordinary SRR unit cell. It is observed that the presence of the additional micro-splits leads to the increase of resonance frequency by substantial amounts due to the series capacitance effect. Next, we have designed and constructed 2 x 2 homogeneous arrays of magnetic resonators which consist of the same type of cells (either A, or B, or C). Such MSSRR blocks are found to provide only a single frequency band of operation around the magnetic resonance frequency of the related unit cell structure. Finally, we have designed and constructed 2 x 2 and 3 x 2 inhomogeneous arrays which contain columns of different types of metamaterial unit cells. We have shown that these inhomogeneous arrays provide two or three different frequency bands of operations due to the use of different magnetic resonators together. The number of additional micro-splits in a given MSSRR cell can be interactively controlled by various switching technologies to modify the overall metamaterial topology for the purpose of activating different sets of multiple resonance frequencies. In this context, use of electrostatically actuated RF MEMS switches is discussed, and their implementation is suggested as a future work, to control the states of micro-splits in large MSSRR arrays to realize tunable multi-band metamaterials.

A SYMMETRIC SURFACE MICROMACHINED GYROSCOPE WITH DECOUPLED OSCILLATION MODES

This paper reports a new symmetric gyroscope structure that allows both matched resonant frequencies for the drive and sense vibration modes for better sensitivity, and also decoupled drive and sense oscillation modes for preventing unstable operation due to mechanical coupling and achieving a low zero-rate output drift. The symmetry and decoupling features are achieved at the same time with a new suspension beam design. The gyroscope structure is designed using a standard three-layer polysilicon surface micromachining process (MUMPS) and simulated using the MEMCAD software. The drive and sense mode resonant frequencies of the fabricated device are measured as 28,535 and 30,306 Hz, respectively, which are in agreement with the finite element simulations. The small mismatch is due to the unsymmetric distribution of the etch holes, which can be eliminated with a proper design. When the resonant frequencies are closely matched, the rate sensitivity of the gyroscope is amplified by the mechanical quality factor of the sense resonant mode. The new suspension beam structure also provides very high quality factors for the drive and sense modes, such as 10,400, when operated under 10 mTorr vacuum level. Even though the performance of the fabricated sensor is limited due to large parasitic capacitances between the mechanical structure and the substrate, measurements, and calculations show that the sensor can still sense angular rates as small as 1.6°/s under vacuum. This sensitivity can be enhanced by at least an order of magnitude if the parasitic capacitances could have effectively been eliminated. The advantage of the new structure can be combined with advanced, high-aspect ratio fabrication processes to obtain very sensitive micromachined gyroscopes.

Long term chronic recordings from peripheral sensory fibers using a sieve electrode array

The use of an implanted micromachined silicon sieve electrode array to make long term chronic recordings from the glossopharyngeal nerve is described. The implant consists of an array of small holes in a silicon substrate, four of which are surrounded by electrodes connected with an integrally fabricated ribbon cable to a percutaneous headcap. Using this device we have been able to monitor the integrity of the electrodes from the time of implantation and subsequently to record evoked sensory responses from mechanoreceptors on the tongue.

Quadrature-Error Compensation and Corresponding Effects on the Performance of Fully Decoupled MEMS Gyroscopes

This paper presents experimental data about the sources of the quadrature error in a fully decoupled microelectromechanical systems gyroscope and demonstrates the extent of performance improvement by the cancellation of this error. Quadrature sources including mass, electrostatic-force, and mechanical-spring imbalances have been compared by FEM simulations, and spring imbalance has been found as the dominant source of the quadrature error. Gyroscopes have been designed with intentional spring imbalances and fabricated with a SOI-based silicon-on-glass fabrication process, the resulting quadrature outputs of the fabricated gyroscopes have been measured, and their agreement with FEM simulations has been verified. Next, it has been experimentally shown that the electrostatic nulling of the quadrature error with closed-loop control electronics improves the bias instability and angle random walk (ARW) of a fully decoupled gyroscope up to ten times. Moreover, the quadrature cancellation improves the scale-factor turn-on repeatability about four times and linearity about 20 times, reaching down to 119 and 86 ppm, respectively. Finally, the quadrature cancellation allows operating the gyroscope with higher drive-mode displacement amplitudes for an increased rate sensitivity. With this technique, outstanding bias instability and ARW performances of 0.39°/h and 0.014 °/√h, respectively, have been achieved.

A Compact Angular Rate Sensor System Using a Fully Decoupled Silicon-on-Glass MEMS Gyroscope

This paper presents the development of a compact single-axis angular rate sensor system employing a 100- mum-thick single-crystal silicon microelectromechanical systems gyroscope with an improved decoupling arrangement between the drive and sense modes. The improved decoupling arrangement of the gyroscope enhances the robustness of sensing frame against drive-mode oscillations and therefore minimizes mechanical crosstalk between the drive and sense modes, yielding a small bias instability. The gyroscope core element is fabricated by through-etching a 100-mum -thick silicon substrate which is anodically bonded to a recessed glass handling substrate. A patterned metal layer is included at the bottom of the silicon substrate, both as an etch-stop layer and a heat sink to prevent heating- and notching-based structural deformations encountered in deep dry etching in the silicon-on-glass process. The fabricated-gyroscope core element has capacitive actuation/sensing gaps of about 5 mum yielding an aspect ratio close to 20, providing a large differential sense capacitance of 18.2 pF in a relatively small footprint of 4.6 mm times 4.2 mm. Excitation and sensing electronics of the gyroscope are constructed using off-the-shelf integrated circuits and fit in a compact printed circuit board of size 54 mm times 24 mm. The complete angular rate sensor system is characterized in a vacuum ambient at a pressure of 5 mtorr and demonstrates a turn-on bias of less than 0.1 deg/s, bias instability of 14.3 deg/h, angle random walk better than 0.115 deg/radic(h), and a scale-factor nonlinearity of plusmn0.6% in full-scale range of plusmn50 deg/s. [2007-0158].