Tianhong Cui

All-polymer capacitor fabricated with inkjet printing technique

Abstract All-polymer capacitors have been fabricated only by the inkjet printing technique. A conductive polymer, poly(3,4-ethylenedioxythiophene), has been employed as the electrode material of the capacitor. A precursor-route polyimide was applied as the insulator of the device. The fabrication process of the inkjet printed all-polymer capacitor has been demonstrated. The electrical characteristics of the polymer capacitor, analogous to that of the common parallel plate capacitor, are discussed in detail. The all-polymer capacitor has been applied to the polymer RC filter circuits. The characteristics of the inkjet printed polymer RC filter are also demonstrated.

An ultrasensitive and low-cost graphene sensor based on layer-by-layer nano self-assembly

The flexible cancer sensor based on layer-by-layer self-assembled graphene reported in this letter demonstrates features including ultrahigh sensitivity and low cost due to graphene material properties in nature, self-assembly technique, and polyethylene terephthalate substrate. According to the conductance change of self-assembled graphene, the label free and labeled graphene sensors are capable of detecting very low concentrations of prostate specific antigen down to 4 fg/ml (0.11 fM) and 0.4 pg/ml (11 fM), respectively, which are three orders of magnitude lower than carbon nanotube sensors under the same conditions of design, manufacture, and measurement.

All-polymer RC filter circuits fabricated with inkjet printing technology

Abstract All-polymer RC filter circuits by all-inkjet printing technology are fabricated for the first time. Conductive polymers such as polyaniline and poly(3, 4-ethylenedioxythiophene) have been used as the electrode material of the capacitor as well as the resistor material. The fabrication process and the characteristics of the printed capacitor and RC filter have been demonstrated. Simulation of the printed RC circuit has been demonstrated and compared with the experimental measurement results. A detail discussion has been given about the all-polymer capacitor and RC filter.

Humidity sensitivity of multi-walled carbon nanotube networks deposited by dielectrophoresis

This paper presents an investigation on the humidity sensitivity of deposited multi-walled carbon nanotube (MWCNT) networks using ac dielectrophoresis (DEP) between interdigitated electrodes (IDEs). MWCNTs dispersed in ethanol were trapped and enriched between IDEs on a Si/SiO2 substrate under a positive DEP force. After the DEP process, the ethanol was evaporated and the MWCNT network on a substrate with IDEs was put into a furnace for repeated thermal annealing. It was found that the resistance stability of the network was effectively improved through thermal annealing. The humidity sensitivity was obtained by measuring the resistance of the MWCNT network with different relative humidity at room temperature. The experimental results show the resistance increases linearly with increasing the relative humidity from 25% to 95% RH with a sensitivity of 0.5%/%RH. The MWCNT networks have a reversible humidity sensing capacity with response time and recovery time of about 3 s and 25 s, respectively. The resistance is dependent on temperature with a negative coefficient of about −0.33%/K in a temperature range from 293 K to 393 K.

Fabrication of high-aspect-ratio polymer-based electrostatic comb drives using the hot embossing technique

We report on the formation of a lateral comb drive on poly-methyl-meth-acrylate (PMMA) using the hot embossing technique. A hot embossing mold insert is fabricated on a silicon wafer by means of lithography and inductive coupled plasma dry etching. The comb drive microstructure is hot embossed under a molding force of 35000 N at 130 °C. We demonstrate the comb drive, 80 units of interdigitated parallel capacitors with the finger gap and width both being 10 μm. The minimum feature size is 5 μm and the thickness of the structure is 60 μm, which makes the aspect ratio 12:1. The comb drive strokes 5 μm under an actuation potential of 180 V. We also present a brief description of the design and simulation with ANSYS.

Low-cost, transparent, and flexible single-walled carbon nanotube nanocomposite based ion-sensitive field-effect transistors for pH/glucose sensing.

Low-cost, transparent, and flexible ion-sensitive field-effect transistors (ISFETs) are presented as pH and glucose sensors. Single-walled carbon nanotubes (SWCNTs) and poly(diallyldimethyammonium chloride, PDDA) are deposited by layer-by-layer (LbL) self-assembly between two metallic electrodes patterned on a polyethylene terephthalate substrate. The pH ISFETs are characterized based on the fact that the electronic conductance of SWCNTs nanocomposite is determined by molecular protonation/deprotonation of carboxylic groups on SWCNTs and by the external Ag/AgCl reference gate voltage. Glucose is detected by the local pH change in the vicinity of SWCNTs with the aid of glucose oxidase (GOx) enzyme. The glucose sensor shows a sensitivity of 18-45 microA/mM on a linear range of 2-10 mM. The apparent Michaelis-Menten constant is 14.2 mM, indicating a high affinity of LbL assembled GOx to glucose. The LbL self-assembly of nanomaterials and enzymes on the transparent and flexible substrate suggests various chemical and biological sensors suitable for in vivo application.

Dual-gate pentacene organic field-effect transistors based on a nanoassembled SiO2 nanoparticle thin film as the gate dielectric layer

In this paper, we report the fabrication of dual-gate organic field-effect transistors (OFETs) using self-assembled SiO2 and thermal oxide as gate dielectric materials and pentacene as a semiconductor. The top dielectric layer was formed by the low-cost and low-temperature self-assembly with SiO2 nanoparticles 45nm in diameter. The fabricated dual-gate pentacene field-effect transistor (FET) has a threshold voltage of −2.2V, a field-effect mobility of 0.1cm2∕Vs, an Ion∕off ratio of 3.8×103, and a slope of 1.3V∕decade. Compared to a single gate OFET, dual-gate FET has better performance with higher drain output current at the relatively low operating voltage, larger field-effect mobility, and better channel controllability by separately adjusting two gate biases.

Fabrication and electrical characteristics of polymer-based Schottky diode

Abstract Metal/polymer Schottky diodes have been fabricated using spin-coated poly(3,4-ethylenedioxythiophene) (PEDT) doped with poly(styrenesulfonate) (PSS) as the p-type semiconductor and aluminum as the metal. The current–voltage and capacitance–voltage characteristics have been studied at room temperature. The breakdown voltage and rectification ratio of the Al/PEDT Schottky diode are about 5.5 V and 1.3×10 4 , respectively. A modified Norde function combined with conventional forward I – V method was used to extract the parameters including barrier height, rectification ratio, ideality factor, as well as the series resistance. This new method allows extraction of device characteristics from measured I – V curve that deviates from ideal I – V curve caused by series resistance.

Bone formation on carbon nanotube composite

The effects of a layer-by-layer assembled carbon nanotube composite (CNT-comp) on osteoblasts in vitro and bone tissue in vivo in rats were studied. The effects of CNT-comp on osteoblasts were compared against the effects by commercially pure titanium (cpTi) and tissue culture dishes. Cell proliferation on the CNT-comp and cpTi were similar. However, cell differentiation, measured by alkaline phosphatase activity and matrix mineralization, was better on the CNT-comp. When implanted in critical-sized rat calvarial defect, the CNT-comp permitted bone formation and bone repair without signs of rejection or inflammation. These data indicate that CNT-comp may be a promising substrate for use as a bone implant or as a scaffold for tissue engineering.

High-mobility transistors based on nanoassembled carbon nanotube semiconducting layer and SiO2 nanoparticle dielectric layer

The authors report the fabrication and characterization of high-mobility thin-film transistors (TFTs) using layer-by-layer (LBL) nano self-assembled single-walled carbon nanotubes (SWCNTs) as the semiconducting material and SiO2 nanoparticles as the gate dielectric material. The channel length and the effective thickness of the SWCNT semiconductor layer are 50μm and 38nm, respectively. The effective thickness of the SiO2 dielectric layer is 180nm. The SWCNT TFT exhibits p-type semiconductor characteristics and operates in the accumulation mode, with a hole mobility (μp) of 168.5cm2∕Vs, a normalized transconductance (gm∕W) of 0.5S∕m, a threshold voltage (Vth) of −3V, and an on/off current ratio (Ion∕off) of 4.2. The combination technique with LBL nano self-assembly and microlithography provides a simple, low-temperature, and highly efficient approach to fabricate inexpensive TFT devices.