Yue Ruifeng

Characterization of Uncooled Poly SiGe Microbolometer for Infrared Detection

An uncooled poly SiGe microbolometer for infrared detection has been fabricated and characterized. The poly SiGe thin film is deposited by ultrahigh vacuum chemical vapour deposition (UHVCVD) system and its structural properties are characterized by Rutherford backscattering spectrometry (RBS) and Raman. The dependences of the temperature coefficient of resistance on operation temperature and on annealing temperature have been investigated. A leg-supported microbridge is used to decrease the thermal conductance of microbolometer with the silicon micromachining technique. The results show that at a chopping frequency of 15 Hz and a bias voltage of 5 V, the maximum detectivity of 8.3×108 cm Hz1/2/W is achieved with a thermal response time of 16.6 ms.

Demonstration of Four Fundamental Operations of Liquid Droplets for Digital Microfluidic Systems Based on an Electrowetting-on-Dielectric Actuator

An electrowetting-on-dielectric actuator is developed, in which the liquid is sandwiched between top and bottom plates. For the bottom plate, silicon wafer is used as the substrate, the heavily phosphorus-doped polysilicon film is deposited by low pressure chemical vapour deposition as the microelectrode array, and thermally grown SiO2 film as the dielectric layer. The top plate is a glass plate covered with transparent and conductive indium tin oxide as the ground electrode. In addition, a Teflon(R) AF1600 film is spun on the surface of both the plates as the hydrophobic layer. The experimental results show that when the gap height between two plates is 133 μm, a prototype of the device is capable of creating, transporting, merging and dividing droplets of deionized water in an air environment with a 70 V at 10 Hz voltage pulse. This is also established by simulations using the computational fluidic software of CFD-ACE+.

Droplet creator based on electrowetting-on-dielectric for lab on a chip

Electrowetting-on-dielectric (EWOD) is to directly control the wettability of liquids on the solid surface by applying the electric potential to the microelectrode array under the dielectric layer. The prototype of the EWOD droplet creator with the sandwiched structure is used: the droplet is sandwiched between the top and bottom plates; the bottom plate consists of silicon used as the substrate of the microelectrode array, nitride silicon film deposited by low pressure chemical vapor deposition as the dielectric layer and the fluorocarbon polymer film deposited by inductively coupled plasma chemical vapor deposition as the hydrophobic layer; and the top plate is the transparent electrode covered with the hydrophobic layer. To obtain the required minimum voltage, the process and the criterion of creating droplets are analyzed. At the voltage of 35 V the deionized water droplet surrounded in silicone oil is successfully created.

Droplets actuating chip based on electrowetting-on-dielectric

A droplet-based actuating chip by using the method of electrowetting-on-dielectric (EWOD) was developed to manipulate the microfluidics. Here, the actuation mechanism of the sandwiched-configuration EWOD chips was carefully studied, and the movement of droplets was numerically analyzed by using the computational fluidic software, CFD-ACE+. The fabrication of the chip, including a heavily phosphorus-doped poly-silicon micro-electrode array and a thermally grown SiO2 dielectric layer, was exploited to improve the chip stability and decrease the actuation voltage. In experiments, the transportation of a deionized droplet of about 0.5 μL is successfully achieved in air by applying the low voltage of 45 V.

Integrated a-Si:B Microbolometer Arrays Based on Improved Porous Silicon Micromachining Techniques

A monolithic uncooled 8×8 microbolometer array with boron-doped a-Si (a-Si:B) thermistors as active elements is presented. The a-Si:B film was deposited by plasma enhanced chemical vapour deposition. To decrease the thermal conductance of the microbolometer, a-Si:B thermistor was formed on a four-leg suspended microbridge. The improved porous silicon micromachining techniques described here enable the integration of the sensor array with the metal–oxide–semiconductor readout circuitry. The sacrificial material of porous silicon is prepared in the first step. It is then well protected all the time during the fabrication of metal–oxide–semiconductor field effect transistors and microbolometers before being released. Measurements and calculations show that the uncorrected uniformity of the 8×8 microbolometer array is about 4.5%, and the detectivity of 2.17×108 cm Hz1/2W−1 is achieved at a chopping frequency of 30 Hz and a bias voltage of 5 V with a thermal response time of 12.4 ms.

Blue-Green Light Emission from a-SiCx:H-Based Fabry–Perot Microcavities

A Si-based novel Fabry–Perot microcavity device that can emit blue-green light at room temperature is proposed and fabricated. One of its Bragg reflectors consists of periodically stacked a-SiO2/a-Si:H layers deposited on the glass by plasma enhanced chemical vapour deposition. The other reflector is a sputtered Al film. The active region between both the reflectors is constructed by a p-type a-SiCx:H/intrinsic-type a-SiCx:H junction from which the electroluminescence (EL) is originated. The EL spectra of this device are recorded by RENISHAW RM2000, a sharp and strong EL peak at 483 nm with FWHM of 20 nm is observed when the device is driven by dc voltages of 8 V, 12 V and 18 V at room temperature. The intensity of EL increases with the applied voltage while the luminescence wavelength keeps unchanged. Compared with the EL spectra from the sample without the Bragg reflector, the luminescence intensity is about 10 times enhanced and the peak is narrowed greatly. The luminescence mechanism is analysed in detail.

MOSFET differential amplifier with input pair and active load pair being stress-sensitive both

The principles of stress sensitive differential amplifier (SSDA) are studied in detail, and a new idea of designing SSDA is presented. Using this idea, the sensitivity of the SSDA can be doubled without any extra cost in area, power, circuit complexity, etc. A HSPICE simulation result is also presented.

EWOD-based variable-focus liquid lens

A variable-focus liquid lens based on EWOD (electrowetting on dielectric) has been developed. It comprises a top glass plate, a ground-electrode-involved bottom glass plate and a counter-electrode-involved cylindrical glass housing which contains two immiscible fluids of air and water with different refractive indices. By changing the applied voltage across the electrodes, we can tune the meniscus between the two fluids and focus length of the lens. The experimental results show that the prototype of the liquid lens could refocus on objects from 2 centimeters up to infinity away within 10 ms using a direct voltage within 40V

Accelerometer Design Using MOS Ring Oscillator

A digital accelerometer is developed by using a ring oscillator (RO) and a mixer. The sensitive unit of the accelerometer is the metal-oxide semiconductor (MOS) ROs located on silicon beams. Based on the piezoresistive effect of the MOS RO, the accelerometer transduces the acceleration into frequency output. The syntonic frequency of the MOS RO changes in relation to many environmental elements, such as temperature, source voltage, and so on. The mixer is an interior signal processor that improves the output signal characteristics, with the digital output signal representing the frequency change. As the accelerometer is based on the piezoresistive effect of the MOS RO, the frequency characteristics of the MOS RO and its relationship with the acceleration are described. The device has been fabricated using standard integrated circuits processing methods combined with the Micro-Electro-Mechanical Systems process. The characteristics of the sample chip are in agreement with the theoretical predictions. The accelerometer has a high sensitivity of 6.91 kHz/g, a low temperature coefficient, and a simple fabrication process.