Kunnyun Kim

A silicon-based flexible tactile sensor for ubiquitous robot companion applications

We present the fabrication process and characteristics of a 3-axes flexible tactile sensor available for normal and shear mode fabricated using Si micromachining and packaging technologies. The fabrication processes for the 3 axes flexible tactile sensor were classified in the fabrication of sensor chips and their packaging on the flexible PCB. The variation rate of resistance was about 2.1%/N and 0.5%/N in applying normal and shear force, respectively. Because this tactile sensor can measure the variations of resistance of the semiconductor strain gauge for normal and shear force, it can be used to sense touch, pressure, hardness, and slip.

Calibration and temperature compensation of silicon pressure sensors using ion-implanted trimming resistors

Abstract A piezoresistive silicon pressure sensor with bipolar on-chip signal conditioning circuits permits offset voltage, full scale span and temperature coefficient of offset voltage and full scale span to be calibrated from a trimming ion-implanted resistors. The ion-implanted resistors with temperature coefficient of 1700 ppm/°C or 4700 ppm/°C were fabricated by the same process as that used for the base and piezoresistors. The fabricated sensor exhibits a sensitivity of 40.5 mV/kPa and temperature coefficient of 46 ppm/°C at the temperature range of −10 to 70°C.

Development of a carbon nanotube-based touchscreen capable of multi-touch and multi-force sensing

A force sensing touchscreen, which detects touch point and touch force simultaneously by sensing a change in electric capacitance, was designed and fabricated. It was made with single-walled carbon nanotubes (SWCNTs) which have better mechanical and chemical characteristics than the indium-tin-oxide transparent electrodes used in most contemporary touchscreen devices. The SWCNTs, with a transmittance of about 85% and electric conductivity of 400 Ω per square; were coated and patterned on glass and polyethyleneterephthalate (PET) film substrates. The constructed force sensing touchscreen has a total size and thickness of 62 mm × 100 mm × 1.4 mm, and is composed of 11 driving line and 19 receiving line channels. The gap between the channels was designed to be 20 µm, taking visibility into consideration, and patterned by a photolithography and plasma etching processes. The mutual capacitance formed by the upper and lower transparent electrodes was initially about 2.8 pF and, on applying a 500 gf force with a 3 mm diameter tip, it showed a 25% capacitance variation. Furthermore, the touchscreen can detect multiple touches and forces simultaneously and is unaffected by touch material characteristics, such as conductance or non-conductance.

Wireless and simultaneous detections of multiple bio-molecules in a single sensor using Love wave biosensor.

A Love wave-based biosensor with a 440 MHz center frequency was developed for the simultaneous detection of two different analytes of Cartilage Oligomeric Matrix Protein (COMP) and rabbit immunoglobulin G (IgG) in a single sensor. The developed biosensor consists of one-port surface acoustic wave (SAW) reflective delay lines on a 41° YX LiNbO3 piezoelectric substrate, a poly(methyl methacrylate) (PMMA) waveguide layer, and two different sensitive films. The Love wave biosensor was wirelessly characterized using two antennas and a network analyzer. The binding of the analytes to the sensitive layers induced a large change in the time positions of the original reflection peaks mainly due to the mass loading effect. The assessed time shifts in the reflection peaks were matched well with the predicted values from coupling of mode (COM) modeling. The sensitivities evaluated from the sensitive films were ∼15 deg/μg/mL for the rabbit IgG and ∼1.8 deg/ng/mL for COMP.

Flexible Tactile Sensor Fabricated using Polymer Membrane

We present the fabrication process and the characteristics of a flexible tactile sensor by silicon micromachining, polymer processing and packaging technologies. The fabrication process for the tactile sensor was composed of in the fabrication of sensor chips and their packaging on the flexible printed circuit board (FPCB). The variation rate of resistance was about 4.6%/N when normal force was applied. This sensor can be used to sense touch, pressure, and slip because the signals are is are determined by the variations of resistance of the metal strain gauge for normal and shear force in tactile sensor.

Flexible heartbeat sensor for wearable device

We demonstrate a flexible strain-gauge sensor and its use in a wearable application for heart rate detection. This polymer-based strain-gauge sensor was fabricated using a double-sided fabrication method with polymer and metal, i.e., polyimide and nickel-chrome. The fabrication process for this strain-gauge sensor is compatible with the conventional flexible printed circuit board (FPCB) processes facilitating its commercialization. The fabricated sensor showed a linear relation for an applied normal force of more than 930 kPa, with a minimum detectable force of 6.25Pa. This sensor can also linearly detect a bending radius from 5mm to 100mm. It is a thin, flexible, compact, and inexpensive (for mass production) heart rate detection sensor that is highly sensitive compared to the established optical photoplethysmography (PPG) sensors. It can detect not only the timing of heart pulsation, but also the amplitude or shape of the pulse signal. The proposed strain-gauge sensor can be applicable to various applications for smart devices requiring heartbeat detection.

Fabrication of Polymer-based Flexible Tactile Sensing Module with Metal Strain Gauges and Interconnecter

We present fabrication of flexible tactile sensing module with NiCr strain gauge as sensing element and interconnecter for signal treatment by polymer MEMS (micro electro mechanical system) technologies using polyimide materials. The tactile sensor array is composed of 16 times 16 sensing elements with 2 mm times 2 mm cell size and its overall size is 4 cm times 5 cm. Both the tactile sensor array and interconnecter are placed in the sensing module during the fabrication process. The fabricated tactile sensing module is measured continuously in the normal force range of 0~1 N with tactile sensor evaluation system. The variation of resistance is relatively increased linearly in the range of 0~0.6 N and saturated after 0.6 N. The variation rate of resistance is approximately 3%/N in the linear range. In addition, the flexibility of the sensing module is adequate to be placed on any curved surface like cylinder because the matrix consists of polymer and metal thin film.

Fabrication of capacitive absolute pressure sensor using Si-Au eutectic bonding in SOI wafer

A capacitive absolute pressure sensor was fabricated using a large deflected diaphragm with a sealed vacuum cavity formed by removing handling silicon wafer and oxide layers from a SOI wafer after eutectic bonding of a silicon wafer to the SOI wafer. The deflected displacements of the diaphragm formed by the vacuum cavity in the fabricated sensor were similar to simulation results. Initial capacitance values were about 2.18pF and 3.65pF under normal atmosphere, where the thicknesses of the diaphragm used to fabricate the vacuum cavity were 20 µm and 30 µm, respectively. Also, it was confirmed that the differences of capacitance value from 1000hPa to 5hPa were about 2.57pF and 5.35pF, respectively.

Fabrication and wafer-level packaging of Si electrostatic microgripper for micro assembly

The wafer-level packaging of an electrostatic Si microgripper was investigated. It is important to ensure safe handling and freedom from damage during fabrication and assembly of micro devices. Some reliability problems have occurred during packaging or handling of the microgripper, regardless of actuation principles. After pre-release of the sacrificial layer, a new wafer-level packaging was processed by anodic bonding between a glass wafer with through-holes and a Si wafer device. A laser dicing has been performed before wire bonding for freedom from damage during both dicing and packaging processes. After the laser dicing, post-releasing has been done. The diced chips were actuated by applied voltage from 0 V/sub dc/ to 15 V/sub dc/. The jaws of the fabricated microgripper have been actuated from 0 /spl mu/m to 25 /spl mu/m.

A flexible strain-gauge sensor for flexible input devices

This study demonstrates a novel polymer-based flexible strain-gauge sensor for flexible input devices in flexible displays. Proposed novel strain-gauge sensor for user interfaces (UIs) in flexible display measures the deformation of an object by using its electrical resistance change. This strain-gauge sensor was fabricated by the double-sided fabrication method with polymer and metal, i.e., polyimide and Nickel-Chrome. Experimental results show that this sensor linearly detects the forces more than 500gf, i.e., 5N, with the force resolution of less than 10gf, i.e., 0.1N. Also it can linearly detect the bending radius from 5mm to 100mm. This flexible strain-gauge sensor array may be positioned on the bezel area of a flexible display device enabling various input methodology as well as UIs.