Nguyen Thanh Tien

A Flexible Bimodal Sensor Array for Simultaneous Sensing of Pressure and Temperature

Diverse signals generated from the sensing elements embedded in flexible electronic skins (e-skins) are typically interfered by strain energy generated through processes such as touching, bending, stretching or twisting. Herein, we demonstrate a flexible bimodal sensor that can separate a target signal from the signal by mechanical strain through the integration of a multi-stimuli responsive gate dielectric and semiconductor channel into the single field-effect transistor (FET) platform.

Highly sensitive stretchable transparent piezoelectric nanogenerators

Here we report a new type of stretchable transparent piezoelectric nanogenerator (NG) using an organic piezoelectric material consisting of poly(vinylidene fluoride trifluoroethylene) [P(VDF-TrFE)] sandwiched with mobility-modified chemical vapor deposition-grown graphene electrodes by ferroelectric polarization into P(VDF-TrFE). This new type of NG has a very high sensitivity and mechanical durability with fully flexible, rollable, stretchable, foldable, and twistable properties. We also investigated the mobility-modified graphene electrodes with ferroelectric P(VDF-TrFE) remnant polarization, and a mechanism is proposed for switching the mobility of the carriers by the ferroelectric remnant polarization. Upon exposure to the same input sound pressure, the measured output performance of the stretchable NG with a thin polydimethylsiloxane stretchable rubber template is up to 30 times that of a normal NG with a plastic substrate. Upon exposure to an air flow at the same speed, the measured output voltage from the stretchable NG is about 8 times larger than that of the normal NG.

Physically Responsive Field-Effect Transistors with Giant Electromechanical Coupling Induced by Nanocomposite Gate Dielectrics

Physically responsive field-effect transistors (physi-FETs) that are sensitive to physical stimuli have been studied for decades. The important issue for separating the responses of sensing materials from interference by other subcomponents in a FET transducer under global physical stimuli has not been completely resolved. In addition, challenges remain with regard to the design and employment of smart materials for flexible physi-FETs with a large electro-physical coupling effect. In this article, we propose the direct integration of nanocomposite (NC) gate dielectrics of barium titanate (BT) nanoparticles (NPs) and highly crystalline poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) into flexible organic FETs to achieve a large electro-physical coupling effect. Additionally, a new alternating current biasing method is proposed for precise extraction and quantification of tiny variations in the remnant polarization of NCs caused by mechanical stimuli. An investigation of physi-FETs under static mechanical stimuli revealed the first ever reported giant, positive piezoelectric coefficients of d(33) up to 960 pC/N in the NCs. The large coefficients are presumably due to the significant contributions of the intrinsic positive piezoelectricity of the BT NPs and P(VDF-TrFE) crystallites.

Reduction of Electrical Hysteresis in Cyclically Bent Organic Field Effect Transistors by Incorporating Multistack Hybrid Gate Dielectrics

We have fabricated flexible organic field effect transistors (OFETs) on polyimide substrate with low hysteresis and low leakage current under repetitive bending. The insertion of an ultrathin atomic-layer-deposited Al 2 O 3 layer in between spin-coated poly-4-vinyl phenol organic layers in a multistack hybrid gate dielectric for OFETs significantly improved stability in the electrical hysteresis during cyclic bending. The observed hysteresis stability for cyclically bent multistack hybrid OFET devices was attributed to efficient blocking of charges injected from the gate electrode due to improved mechanical stability. Cyclically bent samples showed no cracking for thinner Al 2 O 3 layers in the multistack hybrid gate dielectrics.

Effects of piezoresistivity of pentacene channel in organic thin film transistors under mechanical bending

In this report, the electrical properties of both pentacene thin-film and pentacene organic thin-film transistors (OTFTs) under static and dynamic bending were investigated. From the responses to the applied static strain, the piezoresistivity coefficient of pentacene thin-film was determined to be 12.5. Significant changes in the field-effect mobility, μ, and the channel current, which were ascribed to the piezoresistivity of the pentacene channel in OTFTs, were observed while other parameters, such as contact resistance and gate capacitance, appear invariant up to the bending radius of 4.3 mm. Hysteresis in cyclic bending, which was assumed to be caused by local defects of pentacene thin-film, was observed to be independent of bending speed during dynamic bending tests.