Ching-Liang Dai

Fabrication and characterization of CMOS-MEMS thermoelectric micro generators.

This work presents a thermoelectric micro generator fabricated by the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and the post-CMOS process. The micro generator is composed of 24 thermocouples in series. Each thermocouple is constructed by p-type and n-type polysilicon strips. The output power of the generator depends on the temperature difference between the hot and cold parts in the thermocouples. In order to prevent heat-receiving in the cold part in the thermocouples, the cold part is covered with a silicon dioxide layer with low thermal conductivity to insulate the heat source. The hot part of the thermocouples is suspended and connected to an aluminum plate, to increases the heat-receiving area in the hot part. The generator requires a post-CMOS process to release the suspended structures. The post-CMOS process uses an anisotropic dry etching to remove the oxide sacrificial layer and an isotropic dry etching to etch the silicon substrate. Experimental results show that the micro generator has an output voltage of 67 μV at the temperature difference of 1 K.

Manufacture of a Polyaniline Nanofiber Ammonia Sensor Integrated with a Readout Circuit Using the CMOS-MEMS Technique

This study presents the fabrication of a polyaniline nanofiber ammonia sensor integrated with a readout circuit on a chip using the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and a post-process. The micro ammonia sensor consists of a sensing resistor and an ammonia sensing film. Polyaniline prepared by a chemical polymerization method was adopted as the ammonia sensing film. The fabrication of the ammonia sensor needs a post-process to etch the sacrificial layers and to expose the sensing resistor, and then the ammonia sensing film is coated on the sensing resistor. The ammonia sensor, which is of resistive type, changes its resistance when the sensing film adsorbs or desorbs ammonia gas. A readout circuit is employed to convert the resistance of the ammonia sensor into the voltage output. Experimental results show that the sensitivity of the ammonia sensor is about 0.88 mV/ppm at room temperature.

Capacitive micro pressure sensor integrated with a ring oscillator circuit on chip.

The study investigates a capacitive micro pressure sensor integrated with a ring oscillator circuit on a chip. The integrated capacitive pressure sensor is fabricated using the commercial CMOS (complementary metal oxide semiconductor) process and a post-process. The ring oscillator is employed to convert the capacitance of the pressure sensor into the frequency output. The pressure sensor consists of 16 sensing cells in parallel. Each sensing cell contains a top electrode and a lower electrode, and the top electrode is a sandwich membrane. The pressure sensor needs a post-CMOS process to release the membranes after completion of the CMOS process. The post-process uses etchants to etch the sacrificial layers, and to release the membranes. The advantages of the post-process include easy execution and low cost. Experimental results reveal that the pressure sensor has a high sensitivity of 7 Hz/Pa in the pressure range of 0–300 kPa.

A maskless post-CMOS bulk micromachining process and its application

This work investigates a post-CMOS (complementary metal-oxide semiconductor) bulk micromachining process for fabricating suspended microstructures. The advantage of the post-CMOS process is easy execution with low-cost maskless wet etching. The post-CMOS process involves wet etching to remove sacrificial layers, which are stacked layers formed from metal and via layers, to expose the silicon substrate. Then, KOH solution is employed to etch the silicon substrate to develop deep cavities and generate suspended structures. Many suspended structures, which include bridges and plates, are fabricated using the post-CMOS bulk micromachining process. With the same process, two devices that are a suspended micro inductor and a micro hot plate are manufactured successfully. Experimental results reveal that the maximum quality factor of the suspended micro inductor is 4.8 at 4 GHz, and the micro hot plate can generate a high temperature of 300 °C with an applied voltage of 4 V, which has excellent thermal isolation and heating effect.

Polypyrrole Porous Micro Humidity Sensor Integrated with a Ring Oscillator Circuit on Chip

This study presents the design and fabrication of a capacitive micro humidity sensor integrated with a five-stage ring oscillator circuit on chip using the complimentary metal oxide semiconductor (CMOS) process. The area of the humidity sensor chip is about 1 mm2. The humidity sensor consists of a sensing capacitor and a sensing film. The sensing capacitor is constructed from spiral interdigital electrodes that can enhance the sensitivity of the sensor. The sensing film of the sensor is polypyrrole, which is prepared by the chemical polymerization method, and the film has a porous structure. The sensor needs a post-CMOS process to coat the sensing film. The post-CMOS process uses a wet etching to etch the sacrificial layers, and then the polypyrrole is coated on the sensing capacitor. The sensor generates a change in capacitance when the sensing film absorbs or desorbs vapor. The ring oscillator circuit converts the capacitance variation of the sensor into the oscillation frequency output. Experimental results show that the sensitivity of the humidity sensor is about 99 kHz/%RH at 25 °C.

An approach to fabricating microstructures that incorporate circuits using a post-CMOS process

This study proposes a method of fabricating microstructures that incorporate circuits using a standard CMOS (complementary metal oxide semiconductor) process and a post-process. The post-process has two main steps. One uses a photoresist (PR) mask to protect the bonding pads, the circuits and the unneeded etched regions in the chip. The other step employs CF4/O2 RIE (reactive ion etching) and SF6/O2 RIE to etch the sacrificial layers to release the suspended microstructures. A 5.8 GHz low-noise amplifier (LNA) was employed to verify whether the post-process affects the performance of the circuits or not. The test results indicated that the performance of the LNA was the same before and after the post-process, proving that the post-process did not change the functionality of the circuits. Hence, the advantage of the post-process is that it does not damage the bonding pads, the passivation layers and the circuits, which are protected by the PR mask.

Modeling and fabrication of a microelectromechanical microwave switch

A microelectromechanical microwave switch manufactured by using a complementary metal oxide semiconductor (CMOS) post-process has been implemented. An equivalent circuit model is proposed to analyze the performance of the microwave switch. The components of the microwave switch consist of a coplanar waveguide (CPW), a suspended membrane and supported springs. The post-process requires only one wet etching to etch the sacrificial layer, and to release the suspended structures. Experimental results show that the switch has an insertion loss of -2dB at 50GHz and an isolation of -15dB at 50GHz. The driving voltage of the switch approximates to 19V.

Modeling and Manufacturing of Micromechanical RF Switch with Inductors

This study presents the simulation, fabrication and characterization of micromechanical radio frequency (RF) switch with micro inductors. The inductors are employed to enhance the characteristic of the RF switch. An equivalent circuit model is developed to simulate the performance of the RF switch. The behaviors of the micromechanical RF switch are simulated by the finite element method software, CoventorWare. The micromechanical RF switch is fabricated using the complementary metal oxide semiconductor (CMOS) and a post-process. The post-process employs a wet etching to etch the sacrificial layer, and to release the suspended structures of the RF switch. The structure of the RF switch contains a coplanar waveguide (CPW), a suspended membrane, eight springs and two inductors in series. Experimental results reveal that the insertion loss and isolation of the switch are 1.7 dB at 21 GHz and 19 dB at 21 GHz, respectively. The driving voltage of the switch is about 13 V.

Modeling and Fabrication of Micro FET Pressure Sensor with Circuits

This paper presents the simulation, fabrication and characterization of a micro FET (field effect transistor) pressure sensor with readout circuits. The pressure sensor includes 16 sensing cells in parallel. Each sensing cell that is circular shape is composed of an MOS (metal oxide semiconductor) and a suspended membrane, which the suspended membrane is the movable gate of the MOS. The CoventorWare is used to simulate the behaviors of the pressure sensor, and the HSPICE is employed to evaluate the characteristics of the circuits. The pressure sensor integrated with circuits is manufactured using the commercial 0.35 μm CMOS (complementary metal oxide semiconductor) process and a post-process. In order to obtain the suspended membranes, the pressure sensor requires a post-CMOS process. The post-process adopts etchants to etch the sacrificial layers in the pressure sensors to release the suspended membranes, and then the etch holes in the pressure sensor are sealed by LPCVD (low pressure chemical vapor deposition) parylene. The pressure sensor produces a change in current when applying a pressure to the sensing cells. The circuits are utilized to convert the current variation of the pressure sensor into the voltage output. Experimental results show that the pressure sensor has a sensitivity of 0.032 mV/kPa in the pressure range of 0-500 kPa.

A Micromachined Microwave Switch Fabricated by the Complementary Metal Oxide Semiconductor Post-Process of Etching Silicon Dioxide

In this study, we investigate the fabrication of a micromachined microwave switch using the commercial 0.35 µm double polysilicon four metal (DPFM) complementary metal oxide semiconductor (CMOS) process and the post-process of only one maskless wet etching. The post-process has merits of easy execution and low cost. The post-process uses an etchant (silox vapox III) to etch the silicon dioxide layer to release the suspended structures of the microwave switch. The microwave switch is a capacitive type that is actuated by an electrostatic force. The components of the microwave switch are coplanar waveguide (CPW) transmission lines, a suspended membrane and supported springs. Experimental results show that the driving voltage of the switch is about 17 V. The switch has an insertion loss of -2.5 dB at 50 GHz and an isolation of -15 dB at 50 GHz.