Euisik Yoon

A Flexible Polymer Tactile Sensor: Fabrication and Modular Expandability for Large Area Deployment

In this paper, we propose and demonstrate a modular expandable capacitive tactile sensor using polydimethylsiloxsane (PDMS) elastomer. A sensor module consists of 16times16 tactile cells with 1 mm spatial resolution, similar to that of human skin, and interconnection lines for expandability. The sensor has been fabricated by using five PDMS layers bonded together. In order to customize the sensitivity of a sensor, we cast PDMS by spin coating and cured it on a highly planarized stage for uniform thickness. The cell size is 600times600 mum2 and initial capacitance of each cell is about 180 fF. Tactile response of a cell has been measured using a commercial force gauge having 1 mN resolution and a motorized z-axis precision stage with 100 nm resolution. The fabricated cell shows a sensitivity of 3%/mN within the full scale range of 40 mN (250 kPa). Four tactile modules have been successfully attached by using anisotropic conductive paste to demonstrate expandability of the proposed sensors. Various tactile images have been successfully captured by single sensor module as well as the expanded 32times32 array sensors

Normal and Shear Force Measurement Using a Flexible Polymer Tactile Sensor With Embedded Multiple Capacitors

In this paper, we report a new flexible capacitive tactile sensor array with the capability of measuring both normal and shear force distribution using polydimethylsiloxane (PDMS) as a base material. A tactile cell consists of two thick PDMS layers with embedded electrodes, an air gap, and a pillar structure. The pillar structure is formed at the center of each tactile cell between the air gap under a large bump. There are four capacitors in a cell to decompose the contact force into normal and shear components. Four capacitors are arranged in a square form. If a normal force is applied on the bump, the PDMS layer on the pillar structure is compressed, and the air gap between the top and bottom electrodes decreases, resulting in the increase in all four capacitances. If a shear force is applied, a torque is induced around the pillar. Therefore, the capacitance of the two capacitors increases, whereas that of the other two decreases. The bump and the pillar structure play a critical role to generate a torque for shear force measurement. The sensor has been realized in an 8 x 8 array of unit sensors, and each unit sensor responds to normal and shear stresses in all three axes, respectively. Measurement of a single sensor shows that the full-scale range of detectable force is about 10 mN, which corresponds to 131 kPa in three directions. The sensitivities of a cell measured with a current setup are 2.5%/mN, 3.0%/mN, and 2.9 %/mN for the x-, y-, and z-directions, respectively. Normal and shear force images are also captured from a 4 x 4 array of the fabricated sensor. Distinctive characteristic patterns appear when a shear force is applied to the sensor.

CMOS-compatible surface-micromachined suspended-spiral inductors for multi-GHz silicon RF ICs

Fully CMOS-compatible, highly suspended spiral inductors have been designed and fabricated on standard silicon substrates (1/spl sim/30 /spl Omega//spl middot/cm in resistivity) by surface micromachining technology (no substrate etch involved). The RF characteristics of the fabricated inductors have been measured and their equivalent circuit parameters have been extracted using a conventional lumped-element model. We have achieved a high peak Q-factor of 70 at 6 GHz with inductance of 1.38 nH (at 1 GHz) and a self-resonant frequency of over 20 GHz. To the best of our knowledge, this is the highest Q-factor ever reported on standard silicon substrates. This work has demonstrated that the proposed microelectromechanical systems (MEMS) inductors can be a viable technology option to meet the todays strong demands on high-Q on-chip inductors for multi-GHz silicon RF ICs.

A surface-tension driven micropump for low-voltage and low-power operations

In this paper, we first report a micropump actuated by surface tension based on continuous electrowetting (CEW). We have used the surface-tension-induced motion of a mercury drop in a microchannel filled with an electrolyte as actuation energy for the micropump. This allows low voltage operation as well as low-power consumption. The micropump is composed of a stack of three wafers bonded together. The microchannel is formed on a glass wafer using SU-8 and is filled with electrolyte where the mercury drop is inserted. The movement of the mercury pushes or drags the electrolyte, resulting in the deflection of a membrane that is formed on the second silicon wafer. Another silicon wafer, which has passive check valves and holes, is stacked on the membrane wafer, forming inlet and outlet chambers. Finally, these two chambers are connected through a silicone tube forming the complete micropump. The performance of the fabricated micropump has been tested for various operation voltages and frequencies. We have demonstrated actual liquid pumping up to 70 /spl mu/l/min with a driving voltage of 2.3 V and a power consumption of 170 /spl mu/W. The maximum pump pressure is about 800 Pa at the applied voltage of 2.3 V with an operation frequency of 25 Hz.

A low voltage actuated micromachined microwave switch using torsion springs and leverage

In this paper, a push-pull type microwave switch is proposed, which utilizes torsion springs and leverage for low-voltage operation. The switching operation up to 4 GHz is demonstrated. The actuation voltage is /spl sim/5 V. The insertion loss of /spl sim/1 dB and the isolation as high as /spl sim/40 dB at 1 GHz are achieved by the push-pull operation.

An integrated mass flow sensor with on-chip CMOS interface circuitry

A multielement monolithic mass flow sensor which developed for possible use in automotive and industrial process control applications is reported. The chip illustrates the use of a common microstructure (a thin dielectric window/diaphragm) for the simultaneous measurement of flow velocity (rate), flow direction, gas type, and pressure. These transducers are merged with on-chip interface electronics to amplify and multiplex the transducer signals, control on-chip actuators, perform self-test, reduce the number of external leads required, and demonstrate process compatibility with a p-well CMOS process. The on-chip circuitry also implements a bandgap sensor for the measurement of ambient temperature. Thus, the chip simultaneously monitors all parameters needed for the computation of true mass flow, requires only ten external leads, and delivers high-level buffered output signals. >

Surface micromachined solenoid on-Si and on-glass inductors for RF applications

RF performance of surface micromachined solenoid on-chip inductors fabricated on a standard silicon substrate (10 /spl Omega//spl middot/cm) has been investigated and the results are compared with the same inductors on glass. The solenoid inductor on Si with a 15-/spl mu/m thick insulating layer achieves peak quality (Q-) factor of 16.7 at 2.4 GHz with inductance of 2.67 nH. This peak Q-factor is about two-thirds of that of the same inductor fabricated on glass. The highest performance has been obtained from the narrowest-pitched on-glass inductor, which shows inductance of 2.3 nH, peak Q-factor of 25.1 at 8.4 GHz, and spatial inductance density of 30 nH/mm/sup 2/. Both on-Si and on-glass inductors have been modeled by lumped circuits, and the geometrical dependence of the inductance and Q-factor have been investigated as well.

Real-time measurement of the three-axis contact force distribution using a flexible capacitive polymer tactile sensor

In this paper, we report real-time measurement results of various contact forces exerted on a new flexible capacitive three-axis tactile sensor array based on polydimethylsiloxane (PDMS). A unit sensor consists of two thick PDMS layers with embedded copper electrodes, a spacer layer, an insulation layer and a bump layer. There are four capacitors in a unit sensor to decompose a contact force into its normal and shear components. They are separated by a wall-type spacer to improve the mechanical response time. Four capacitors are arranged in a square form. The whole sensor is an 8 × 8 array of unit sensors and each unit sensor responds to forces in all three axes. Measurement results show that the full-scale range of detectable force is around 0‐20 mN (250 kPa) for all three axes. The estimated sensitivities of a unit sensor with the current setup are 1.3, 1.2 and 1.2%/mN for the x-, y- and z-axes, respectively. A simple mechanical model has been established to calculate each axial force component from the measured capacitance value. Normal and shear force distribution images are captured from the fabricated sensor using a real-time measurement system. The mechanical response time of a unit sensor has been estimated to be less than 160 ms. The flexibility of the sensor has also been demonstrated by operating the sensor on a curved surface of 4 mm radius of curvature. (Some figures in this article are in colour only in the electronic version)

Tools for probing local circuits: high-density silicon probes combined with optogenetics.

To understand how function arises from the interactions between neurons, it is necessary to use methods that allow the monitoring of brain activity at the single-neuron, single-spike level and the targeted manipulation of the diverse neuron types selectively in a closed-loop manner. Large-scale recordings of neuronal spiking combined with optogenetic perturbation of identified individual neurons has emerged as a suitable method for such tasks in behaving animals. To fully exploit the potential power of these methods, multiple steps of technical innovation are needed. We highlight the current state-of-the-art in electrophysiological recording methods, combined with optogenetics, and discuss directions for progress. In addition, we point to areas where rapid development is in progress and discuss topics where near-term improvements are possible and needed.

3-D construction of monolithic passive components for RF and microwave ICs using thick-metal surface micromachining technology

As a viable technological option to address todays strong demands for high-performance monolithic low-cost passive components in RF and microwave integrated circuits (ICs), a new CMOS-compatible versatile thick-metal surface micromachining technology has been developed. This technology enables to build arbitrary three-dimensional (3-D) metal microstructures on standard silicon substrate as post-IC processes at low temperature below 120/spl deg/C. Using this technology, various highly suspended 3-D microstructures have been successfully demonstrated for RF and microwave IC applications. We have demonstrated spiral inductors suspended 100 /spl mu/m over the substrate, coplanar waveguides suspended 50 /spl mu/m over the substrate, and complicated microcoaxial lines, which have 50-/spl mu/m-suspended center signal lines surrounded by inclined ground shields of 100 /spl mu/m in height. The microwave performance of the microcoaxial transmission line fabricated on a glass substrate has been evaluated to achieve very low attenuation of 0.03 dB/mm at 10 GHz with an effective dielectric constant of 1.6. The process variation/manufacturability, mechanical stability, and package issues also have been discussed in detail.