Ming-Zhi Dai

Room-temperature-operated sensitive hybrid gas sensor based on amorphous indium gallium zinc oxide thin-film transistors

An organic sensing layer is capped onto an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) to form a hybrid sensor. The organic layer, served as a second gate, forms a p-n junction with the a-IGZO film. Oxidizing or reducing vapor molecules act like electron acceptors or electron donors to change the potential of the organic layer and the current of a-IGZO TFT. A sensitive and reversible response to 100 ppb ammonia and 100 ppb acetone is obtained at room temperature. This letter opens a route to develop low-cost large-area bio/chemical sensor arrays based on the emerging a-IGZO TFT technology.

Highly Sensitive Ammonia Sensor with Organic Vertical Nanojunctions for Noninvasive Detection of Hepatic Injury

We successfully demonstrate the first solid-state sensor to have reliable responses to breath ammonia of rat. For thioacetamide (TAA)-induced hepatopathy rats, we observe that the proposed sensor can detect liver that undergoes acute-moderate hepatopathy with a p-value less than 0.05. The proposed sensor is an organic diode with vertical nanojunctions produced by using low-cost colloidal lithography. Its simple structure and low production cost facilitates the development of point-of-care technology. We also anticipate that the study is a starting point for investigating sophisticated breath-ammonia-related disease models.

Polymer hot-carrier transistor with low bandgap emitter

Vertical polymer hot-carrier transistor using the low bandgap material poly(3-hexylthiophene) as both the emitter and the collector are studied. The common emitter current gain is shown to depend on the LiF thickness and the emitter thickness, with maximal value at 31. Current density as high as 31mA∕cm2 is achieved when collector voltage is −10V. For the device using blend of poly(3-hexylthiophene) and high bandgap polymer poly(9-vinylcarbazole) as the emitter, the current density rises sharply to 428mA∕cm2. The brightness of 3000cd∕m2 is obtained as a polymer light-emitting diode is driven by the transistor with the same area. The transistor can be operated at 100kHz.

Porous Organic TFTs for the Applications on Real-Time and Sensitive Gas Sensors

A pentacene-based organic thin-film transistor (OTFT) with a porous active layer is demonstrated for the first time. The porous OTFT exhibits a fast, sensitive, and reversible response to ammonia gas with a detection limit as 500 ppb, whereas the OTFT without porous structure has a slow response and a poor recovery behavior. The sensing mechanism dominated by the dissociation of hydroxyl groups of the polymer dielectric layer is raised and discussed. The proposed device is the first OTFT-based ammonia sensor with reversible response and high sensitivity in low parts-per-million range. It is promising for the development of a diagnostic breath analysis system.

Polymer Infrared Proximity Sensor Array

A near-infrared proximity sensor array is achieved by integrating a polymer light-emitting diode and a polymer photodetector (PD). A green emission is converted into deep red peaked at 670 nm by the inorganic phosphor Intematix R670 with quantum efficiency of over 20%. A bandpass filter is used to select a spectral tail of phosphor luminescence with a wavelength above 700 nm. The emissive polymer is green polyfluorene. The infrared PD contains a thick film of a blend of poly(3-hexylthiophene) and (6,6)-phenyl-C61-butyric acid methyl ester up to a thickness of 8 m. Position of a moving object at a distance of 10 cm is detected in real time by the array with dynamic images displayed on the computer screen.

Achieving a good life time in a vertical-organic-diode gas sensor.

In this study, we investigate the keys to obtain a sensitive ammonia sensor with high air stability by using a low-cost polythiophene diode with a vertical channel and a porous top electrode. Poly(3-hexylthiophene) (P3HT) and air-stable poly(5,5′-bis(3-dodecyl-2-thienyl)-2,2′-bithiophene) (PQT-12) are both evaluated as the active sensing layer. Two-dimensional current simulation reveals that the proposed device exhibits numerous connected vertical nanometer junctions (VNJ). Due to the de-doping reaction between ammonia molecules and the bulk current flowing through the vertical channel, both PQT-12 and P3HT VNJ-diodes exhibit detection limits of 50-ppb ammonia. The P3HT VNJ-diode, however, becomes unstable after being stored in air for two days. On the contrary, the PQT-12 VNJ-diode keeps an almost unchanged response to 50-ppb ammonia after being stored in air for 25 days. The improved storage lifetime of an organic-semiconductor-based gas sensor in air is successfully demonstrated.

Detecting breath ammonia for non-invasive diagnostic based on low-cost organic diode with vertical nanojunctions

We propose a novel solid-state electrical ammonia sensor based on a vertical organic diode with high-density nanopores in the top electrode. The proposed ammonia sensor has a detection limit of 20 ppb, a real-time response, sufficient selectivity, simple structure, high reproducibility, and a low production cost. In addition, we used the proposed sensor to detect the nasal breath of rats directly. After controlling the relative humidity and filtering out the CO2, we successfully obtained repeated real-time, reliable responses. This is the first demonstration of a solid-state sensor having reliable responses to the breath ammonia of an animal. The sensing response between normal and acute groups is significantly different (p <; 0.05). These results demonstrated that the proposed ammonia sensor can detect liver that undergoes moderate hepatopathy.