Dae-Sung Lee

Development of Micro-Heaters with Optimized Temperature Compensation Design for Gas Sensors

One of the key components of a chemical gas sensor is a MEMS micro-heater. Micro-heaters are used in both semiconductor gas sensors and NDIR gas sensors; however they each require different heat dissipation characteristics. For the semiconductor gas sensors, a uniform temperature is required over a wide area of the heater. On the other hand, for the NDIR gas sensor, the micro-heater needs high levels of infrared radiation in order to increase sensitivity. In this study, a novel design of a poly-Si micro-heater is proposed to improve the uniformity of heat dissipation on the heating plate. Temperature uniformity of the micro-heater is achieved by compensating for the variation in power consumption around the perimeter of the heater. With the power compensated design, the uniform heating area is increased by 2.5 times and the average temperature goes up by 40 °C. Therefore, this power compensated micro-heater design is suitable for a semiconductor gas sensor. Meanwhile, the poly-Si micro-heater without compensation shows a higher level of infrared radiation under equal power consumption conditions. This indicates that the micro-heater without compensation is more suitable for a NDIR gas sensor. Furthermore, the micro-heater shows a short response time of less than 20ms, indicating a very high efficiency of pulse driving.

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.

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.

Probe-pin device for optical neurotransmitter sensing in the brain

Development of an optical neurotransmitter sensing device using nano-plasmonic probes and a micro-spectrometer for real time monitoring of neural signals in the brain is underway. Clinical application of this device technology is to provide autonomous closed-loop feedback control to a deep brain stimulation (DBS) system and enhance the accuracy and efficacy of DBS treatment. By far, we have developed an implantable probe-pin device based on localized field enhancement of surface plasmonic resonance on a nanostructured sensing domain which can amplify neurochemical signals from evoked neural activity in the brain. In this paper, we will introduce the details of design and sensing performance of a proto-typed microspectrometer and nanostructured probing devices for real time measurement of neurotransmitter concentrations.

A Millimeter-wave Image Sensor using Antenna Coupled Micro Thermocouple

A newly developed millimeter wave detector that adopts a micro dipole antenna as a millimeter wave receiver and a micro thermocouple as a bolometer is presented. The micro-thermocouple and a micro heater were designed to be placed between the two arms of dipole antenna. The incident millimeter wave is converted to a voltage signal by the Seebeck effect of the micro-thermocouple. The thermocouple made of aluminum and polysilicon and the heater made of polysilicon were fabricated on the low stress silicon nitride diaphragm to reduce the surface wave loss and to enhance the thermal isolation. A micromachined silicon reflector was used to improve the gain of the antenna. Also for the better impedance matching, the distance from the antenna to reflector was optimized by simulation and measurement technique. The thermal conductance of the device was measured to be 7.9×10− 5W/K at 10mTorr. The measured resonance frequency was 44GHz and the maximum responsivity was 7.5V/W. The device showed the operating bandwidth of 40∼50GHz for 3dB sensitivity.

High Accuracy Open-Type Current Sensor with a Differential Planar Hall Resistive Sensor

In this paper, we propose a high accuracy open-type current sensor with a differential Planar Hall Resistive (PHR) sensor. Conventional open-type current sensors with magnetic sensors are usually vulnerable to interference from an external magnetic field. To reduce the effect of an unintended magnetic field, the proposed design uses a differential structure with PHR. The differential structure provides robust performance to unwanted magnetic flux and increased magnetic sensitivity. In addition, instead of conventional Hall sensors with a magnetic concentrator, a newly developed PHR with high sensitivity is employed to sense horizontal magnetic fields. The PHR sensor and read-out integrated circuit (IC) are integrated through a post-Complementary metal-oxide-semiconductor (CMOS) process using multi-chip packaging. The current sensor is designed to measure a 1 A current level. The measured performance of the designed current sensor has a 16 kHz bandwidth and a current nonlinearity of under ±0.5%.

Application of Surface Protective Coating to Enhance Environment-Withstanding Property of the MEMS 2D Wind Direction and Wind Speed Sensor

In this study, a microelectromechanical system (MEMS) two-dimensional (2D) wind direction and wind speed sensor consisting of a square heating source and four thermopiles was manufactured using the heat detection method. The heating source and thermopiles of the manufactured sensor must be exposed to air to detect wind speed and wind direction. Therefore, there are concerns that the sensor could be contaminated by deposition or adhesion of dust, sandy dust, snow, rain, and so forth, in the air, and that the membrane may be damaged by physical shock. Hence, there was a need to protect the heating source, thermopiles, and the membrane from environmental and physical shock. The upper protective coating to protect both the heating source and thermopiles and the lower protective coating to protect the membrane were formed by using high-molecular substances such as SU-8, Teflon and polyimide (PI). The sensor characteristics with the applied protective coatings were evaluated.

Technology development of silicon based CMOS tactile senor for robotics applications

This paper describes the design, manufacture and measure of tactile sensor with piezoresistive detection of deflection. The tactile sensor array was constructed with a fully integrated complementary metal oxide semiconductor (CMOS) fabrication process and bulk micromachining for the sensing structures. Electrical connections were made between the flexible printed circuit boards (FPCB) and the sensor array module using an anisotropic conductive film (ACF) bonding. The individual sensor element has been shown to demonstrate linear responses to applied normal stress (117 mV/N). Therefore, this approach could yield a highly sensitive tactile sensor array for use in dexterous robotic applications.