Mao-Chen Liu

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.

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.

Nanoparticle SnO2 Gas Sensor with Circuit and Micro Heater on Chip Fabricated Using CMOS-MEMS Technique

The fabrication of a carbon monoxide (CO) micro gas sensor integrated with an inverting amplifier circuit and a micro heater on chip using the commercial 0.35mum complementary metal oxide semiconductor (CMOS) process and a post-process have been implemented. The gas sensor is composed of a polysilicon resistor and a CO gas sensing film. Tin dioxide prepared by the sol-gel method is adopted as the CO gas sensing film. The micro heater is used to provide the working temperature of the gas sensor. The gas sensor, which is a resistive type sensor, changes the resistance when the sensing film adsorbs CO gas. The inverting amplifier circuit is utilized to convert the resistance of the gas sensor into the voltage output. Experimental results show that the sensitivity of the CO gas sensor is about 1 mV/ppm.

High Q-factor CMOS-MEMS inductor

This study investigates a high Q-factor spiral inductor fabricated by the CMOS (complementary metal oxide semiconductor) process and a post-process. The spiral inductor is manufactured on silicon substrate using the 0.35 mum CMOS process. In order to reduce the substrate loss and enhance the Q-factor of the inductor, silicon substrate under the inductor is removed using a post-process. The post-process uses RIE (reactive ion etching) to etch the sacrificial layer of silicon dioxide, and then TMAH (tetra methyl ammonium hydroxide) is employed to remove the underlying silicon substrate and obtain the suspended spiral inductor. The advantage of the post process is compatible with the CMOS process. The Agilent 8510 C network analyzer and a Cascade probe station are used to measure the performances of the spiral inductor. Experiments indicate that the spiral inductor has a Q-factor of 15 at 11 GHz, an inductance of 4 nH at 25.5 GHz and a self-resonance frequency of about 27 GHz.

Investigation into the Effect of Varied Functional Biointerfaces on Silicon Nanowire MOSFETs

A biocompatible and functional interface can improve the sensitivity of bioelectronics. Here, 3-aminopropyl trimethoxysilane (APTMS) and 3-mercaptopropyl trimethoxysilane (MPTMS) self-assembled monolayers (SAMs) were independently modified on the surface of silicon nanowire metal-oxide-semiconductor field effect transistors (NW-MOSFETs). Those SAMs-modified silicon NW-MOSFETs were used to discriminate various pH solutions and further verify which modified regime was capable of providing better electrical signals. The APTMS-SAM modified NW-MOSFETs showed better electrical responses in pH sensing. Biomolecules on APTMS-SAM modified NW-MOSFETs also gave better signals for the corresponding proteind in physiological buffer solutions. Atomic force microscopy (AFM) clarified those electrical phenomena and found biomolecules on APTMS-SAM were relatively uniformly modified on NW-MOSFETs. Our results showed that more uniform modification contributed to better signal response to protein interactions in physiological buffer solutions. It suggests that suitable surface modifications could profoundly affect the sensing response and sensitivity.

Complementary Metal–Oxide–Semiconductor Microelectromechanical Pressure Sensor Integrated with Circuits on Chip

This study investigates the fabrication of an integrated pressure sensor using the commercial 0.35 µm complementary metal–oxide–semiconductor (CMOS) process and a post-process. The main character of the pressure sensor is to integrate the circuits on a chip. The pressure sensor that is a capacitive type sensor is composed of 128 sensing cells in parallel, and each sensing cell contains a suspended membrane and a fixed electrode to form a parallel-plate sensing capacitor. The circuits are employed to convert the capacitance variation of the pressure sensor into the output voltage. The post-process uses etchants to etch the sacrificial layers to release the suspended membrane of the pressure sensor, and then low pressure chemical vapor deposition (LPCVD) parylene is utilized to seal the etching holes of the pressure sensor. Experimental results show that the pressure sensor has a sensitivity of 1.5 mV/(V·kPa) in the pressure range of 0–200 kPa.

A linearly tunable capacitor fabricated by the post-CMOS process

This work investigates the fabrication of a linearly tunable capacitor using the standard CMOS (Complementary Metal-Oxide Semiconductor) process and a maskless post-process. This tunable capacitor is composed of a comb-drive actuator, a parallel capacitor and supported beams. The comb-drive actuator is employed to change the position of the movable electrode plate in the parallel capacitor, such that the overlap area between the two plates in the parallel capacitor is changed. The capacitance of the tunable capacitor is a linear variation. The benefits of the pos-process are compatible with the CMOS process and etching without mask. The post-process has two main steps. One is the use of phosphoric acid to remove the metal from sacrificial layers and etch holes. The other step employs RIE (reactive ion etching) to etch the passivation layer over the pads. The experimental results show a capacitance of 500 fF, and 50% tuning range at 20 V.

Characterization of functional biointerface on silicon nanowire MOSFET

Biointerface between biological organisms and electronic devices has attracted a lot of attention since a biocompatible and functional interface can revolutionize medical applications of bioelectronics. Here, we used 3-aminopropyl trimethoxysilane (APTMS) self-assembled monolayer (SAM) to modify the surface of nanowire-based metal-oxide-semiconductor field-effect transistors (NW-MOSFETs) for pH sensing and later creation of biointerface. Electrical measurement was utilized to first verify the sensing response of unmodified NW-MOSFETs and then examine pH sensing on APTMS modified NW-MOSFETs. A biointerface was then created by immobilizing polylysine, either poly-D-lysine (PDL) or poly-L-lysine (PLL), on APTMS modified NW-MOSFETs. This biointerface was characterized by electron spectroscopy for chemical analysis (ESCA), cell biocompatibility, and fluorescent images. The results of ESCA verified the amide bonding (CONH) between polylysine and APTMS modified surface. After PC12 cultured on polylysine-APTMS modified area, highly selective areas for cell growth were observed by fluorescent microscope. Analysis and improvement of selectively cell-growth biointerface on the NW-MOSFETs gave us an insight into future development of neuronal biosensors.

The effect of varied functional biointerfaces on the sensitivity of silicon nanowire MOSFET

A biocompatible and functional interface can improve medical applications of bioelectronic. Here, 3-aminopropyl trimethoxysilane (APTMS) and 3-mercaptopropyl trimethoxysilane (MPTMS) self-assembled monolayers (SAMs) were used to modify the surface of silicon nanowire (NW) -MOSFETs. AFM and electrical pH sensing verified which monolayer was capable of performing better electrical signal for subsequent immobilization of biomolecule. APTMS-SAM modified NW-MOSFETs showed more uniform modification on NW-MOSFETs and better electrical response to pH sensing. Biomolecule, such as antibody against prostate-specific antigen (anti-PSA), immobilized on APTMS-SAM modified NW-MOSFETs also successfully sensed those corresponding antigens in electrical measurement system. It elucidated that the suitable surface modification would profoundly affect the sensing response and sensitivity.