Electrical Properties of ZnO Nano-Particles Embedded in Polyimide

The ZnO nano-particles were made in the polyimide dielectric matrix through using the chemical reaction between the zinc metal film and polyamic acid. The concentration of the ZnO particle is about 15 ?— 10^sup 12^ cm^sup -2^ with average size below 10 nm and its shapes are almost spherical. Then, the polyimide layer is a stable dielectric material with a dielectric constant of 29 To investigate the electrical properties of ZnO particles in the polyimide insulator film, we fabricated a metal-insulator-semiconductor (MIS) arrangement and measured capacitance-voltage (C-V) with temperature modulation. At sweep temperature, C-V hysteresis with a voltage gap of 28 V appeared in the MIS make using SiO^sub 2^/Si substrate. As the measuring temperature decreased, the C-V bend s were shifted slightly to the accumulation region with gate bias. It was considered that the electrical charging may be met with dominantly in nanoparticles, having solitary a few defects at the interface of the polyimide/SiO^sub 2^ and the polyimide/ZnO.

Key words: Nano-particle, polyimide matrix, electrical charging, ZnO, metal-insulator-semiconductor (MIS)

INTRODUCTION

Quantum dots (QDs) are nano-sized zero-dimensional configurations in which the motion of an electron is restricted in all directions. In this region, the quantum mechanical issues appear dominantly. Currently, the research of QDs is a main subdue for quantum devices, because the QD are awaited to be applied to quantum bit, single-electron memory devices, etc1-4 From this point of view, the metal-oxide nano-particles embedded in polyimide matrix were fabricated and their electrical properties studied with a nano-floating gated memory device structure56 The metal oxide nano-particles were formed by dint of chemical reaction between metal film and polyamic acid. The metal films were thermal evaporated upon a semiconductor or insulator substrates, and then polyamic acid, precursor of polyimide, was spin coated upon theses films. Sequentially, under the curing proces below 400?°C nano-particles were created by the agency of this chemical reaction and the particle dimensions were between 4 nm and 20 nm This proces is real simple and has some advantages; for instance, it takes a certain number of specific area as possible.

Especially, there has been interest in applying ZnO nano-particles to a short wavelength photonic device based upon its wide band-gap electrical peculiarity The optical absorption due to the quantum size issue was measured from the ZnO particles embedded in polyimide, which means the particle isolation in polyimide matrix.7 Its wide bandgap may be not beneficial for memory devices, but its electronic properties must be investigated for electrical application.

In this research the electrical characteristics by charging in the quantum states and surface deficiencys in metal-insulator-semiconductor (MIS) structures with ZnO nano-particles in the polyimide insulator were examined by the agency of capacitance-voltage (C-V) measurement and temperature-dependent C-V analysis. In this MIS combination of parts to form a whole it appeared that a C-V hysteresis and its application of a nonvolatile nano-floating gate memory were discussed with in relation to the electrical charging issue

EXPERIMENT

The metal-oxide semiconductor nano-particles were formed by means of a chemical reaction between metal thin films and polyamic acid, a precursor of polyimide during the curing proces As a originate the metal films were transformed to metal-oxide nano-particles in the polyimide matrix.4,5 The polyimide used in this close attention was a biphenyltetracarboxylic dianhydride-p-phenylene diamine (BPDA-PDA) with dielectric constant of 29 The Zn thin film was deposited through evaporation with the thickness of 10 nm upon the p-type Si wafer or SiO^sub 2^/Si substrate with SiO^sub 2^ thickness of 135 nm Then, 50-nm-thick polyamic acid was spin coated upon the Zn metal film. The curing proces with 350?°C in the electrical furnace was followed during 1 h below the curing process, the N^sub 2^ atmospheric compressing environment was used to shut up the intervention of oxygen. end the curing process, the polyamic acid layer of 50-nm thickness is transformed into the polyimide film, of about 40 nm in thickness.

Fig. 1 Schematics of MIS forms with nano-particles embedded in polyimide. (a) Metal and polyimide films are deposited upon the p-type Si substrate and (b) a SiO^sub 2^ potential barrier with 135-nm thickness exists between the polyimide layer and the Si substrate.

Finally, depositing the Au metal gate upon the top of the stacked arrangement we were able to fabricate devices with MIS form in which the polyimide capacitor contains metal-oxide nano-particles. Figure 1 exhibits the MIS structure containing the ZnO nano-particles. The C-V measurements were done with a MHz capacitance meter (HP4280A) (Hewlett-Packard) in the temperature range of 15 to 320 K

RESULT AND DISCUSSION

Figure 2a and b exhibit a plane view and a cross-sectional view of transmission electron microscopy (TEM) images for ZnO nano-particles embedded in the polyimide matrix, respectively. In Fig. 2a, the average size of the particle was below 10 nm and its shapes were almost sphere. The concentration of the ZnO particle was about 15 ?— 10^sup 12^ cm^sup -2^ Figure 2b displays the ZnO particles gathered near the original Zn film location.