Elsevier

Thin Solid Films

Volume 483, Issues 1–2, 1 July 2005, Pages 382-387
Thin Solid Films

The preparation of ZnO based gas-sensing thin films by ink-jet printing method

https://doi.org/10.1016/j.tsf.2005.01.015Get rights and content

Abstract

An ink-jet printing technique was applied to prepare ZnO based gas-sensing thin films. ZnO inks with appropriate viscosity and surface tension were prepared by sol-gel techniques, and printed onto substrates using a commercial printer. After the drying and heating treatment processes, continuous ZnO films were formed and studied by scanning electron microscopy, X-ray diffraction and by a home-made gas sensitivity measuring system. It was found that the morphology and electrical properties of the films changed significantly with the thickness of the films, which can be adjusted simply by printing on the film with increasing frequency. Highest resistance and sensitivity to acetone vapor were obtained when the film was prepared by printing only once on it. Different dopants with certain concentrations could be added into the films by printing with different dopant inks and printing frequency. All Pd, Ag, and ZrO2 dopants increased both the resistivity and the sensitivity of the films (180 ppm acetone). This work showed that the ink-jet printing technique was a convenient and low cost method to prepare films with controlled film thickness and dopant concentration.

Introduction

Metal-oxide gas-sensing films had been widely used due to their excellent properties, such as small size, low cost, high sensitivity, fast response and recovery speed. But many problems still exist to be solved for more applications, and a lot of research works are being carried out on these fields to further improve their selectivity, sensitivity and stability. These works include trying new gas-sensing materials, introducing different dopants, fabricating multilayered films, applying network recognition techniques to make electric nose, and utilizing new techniques to prepare sensing films, etc. [1], [2], [3], [4]. Up to now, many methods have been used to prepare gas-sensing films, such as R.F. magnetron sputtering [5], spray pyrolysis [6], metal organic chemical vapor deposition [7], reactive ion-assisted deposition [8], and thermal deposition [9]. However, these methods could not fulfill all the requirements for making high quality sensors, especially when films with complex composition were to be deposited, or many different gas-sensing films were to be integrated on one chip to make an electronic nose.

The ink-jet printing process is a contactless technique of printing, and is widely used for desktop publishing [10], [11]. Recently it was applied successfully in fabricating many functional devices, such as the conjugated polymer device [12], functionally graded material [13], ultra-thin film electrodes [14], thin-film transistors [15], etc.

In this paper, ink-jet printing technique was used to prepare gas-sensing films. The materials to be deposited were dissolved or dispersed in solvent and used as inks, which were adjusted with appropriate surface tension and viscosity, and injected into the cartridge. Commercial ink-jet printing apparatus were used to print the inks directly onto substrates. As more than four kinds of inks could be simultaneously used in printing with a common color ink-jet printer, films with different chemical ingredients could be deposited with controlled patterns at the same time. ZnO based thin films were prepared by this printing technique with respect to printing sequence and ink-doping, and their gas-sensing properties were studied.

Section snippets

Experimental details

The ink-jet printing system, as shown in Fig. 1(a), was composed of a printing device, a sample platform and a control system. The printing head of a commercial color printer was used as the printing device in our system, and four kinds of inks could be simultaneously printed onto the substrate. The platform where the substrates were placed could move in two directions. The printing process and the movement of the platform were controlled by a computer.

All the reagents used were analytical

Microstructure

The XRD pattern of the Al2O3 substrate with interdigital gold electrodes is shown in graph (a) of Fig. 3, while graph (b) shows the XRD pattern of ZnO thin film deposited on the substrate by printing pure ZnO ink (ink A) twice. The peaks at 31.8°, 34.5° and 36.3° were due to the diffraction from the (100), (002) and (101) crystalline plane of wurtzite structure of ZnO respectively, according to the ZnO Joint Committee on Powder Diffraction Standards database (card no. 361451) [16]. As a rough

Conclusion

ZnO based gas-sensing films were successfully prepared by the ink-jet printing technique. The thickness of the films could be controlled conveniently by selecting different printing frequencies. ZnO films with different concentrations of dopant, such as Pd, Ag, and ZrO2, were achieved by printing with corresponding inks. This work indicated that the ink-jet printing method was promising for the preparation of functional material films, especially when a number of films with different

Acknowledgement

This work was supported by the National Important Elemental Research Program (G2000067205-4) and The National High Technology Research and Development Program of P.R. China (2002AA325070).

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