(257t) Development of a Sensing Device with an Integrated Plasmas Generation Unit

This work presents a sensing device with an integrated plasmas generation unit. This device is made of double-sided copper laminate with a 0.05-mm-thick dielectric layer in-between. The electrode patterns are defined by the toner-transfer method, which is an easy-to-fabricate process. The electrode pattern design contains three electrodes: one pair of electrodes patterned on the front side of the device and the third electrode patterned on the back side of the device. The sensing unit uses thick film ZnO, a commonly-used inorganic semiconductor, as the sensing element. The ZnO thick film is deposited at the gap between the paired electrodes on the front side by drop casting or screen printing. The plasma generation device generates atmospheric pressure microplasmas, plasmas with geometric dimension less than 1 mm. This microplasma is a dielectric-barrier-discharge (DBD)-type plasma operated at one atmosphere. The sensing unit is a conductometric-type sensor, which measures the DC resistance of the ZnO thick film across the paired electrodes on the front side. The microplasma is used to treat ZnO for annealing and/or regeneration purposes. When the resistance across the paired electrodes on the front side is measured, this device functions as the sensing mode. When the paired electrodes on the front side are ground and shorted and the back-side electrode is driven by high voltages, the DBD-type microplasma is generated at the gap between the paired electrodes on the front side, where ZnO thick film is deposited. In this mode, ZnO can be treated. Stable plasmas can be sustained in ambient air or argon with high voltage AC with the frequency of 21.5 kHz and the peak-to-peak voltage of up to 3 kV. Preliminary tests show that the resistance of the deposited ZnO thick film ranges from 10⁶ to 10⁹ Ω. After 15 minutes or less microplasma treatment, the resistance reduces by at least 1 order of magnitude. This proves the concept using the integrated plasma generation unit for in-situ and on-demand sensing element treatment.