Low K dielectrics in sintered Al–Zr oxide composites processed by thermal plasma heating

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Abstract

A simple and low cost heating technique based on extended arc thermal plasma heating (EATPH) source has been developed to sinter high temperature Alx–Zr100−x (x=0, 10, 20, …, 100) oxides. Structure and morphology of sintered Al–Zr oxide samples were studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). Interesting result pertaining to the reduction of dielectric constant (K) and dielectric loss (tan δ) were noted in thermal plasma sintered specimen as compared to the conventional sintered sample using resistive heating. It is observed that values of K are reduced up to 40% (maximum) w.r.t. conventional sintering. This low K behavior observed in thermal plasma sintered sample may be attributed to the incorporation of dynamic inclusion in different defect form during thermal plasma heating within a short sintering time. It is also further observed from the frequency and temperature variation of K and tan δ that surface charge polarization along with dipole screening play an important role at high frequencies and temperatures which can be explained by dipole pinning and depinning mechanisms.

Introduction

As of today, the recent advances in the performance of very large scale integrated microelectronic devices have reached the point where multielemental oxides with multilayer metallization and the interlayer dielectric have become the critical limiting factors for device fabrications A new generation of low K materials [1], [2] are required to achieve the advantages in high speed and low power dissipation. Many efforts have been made by researchers over the years to investigate suitable processing of economically viable dielectric materials having a low K value [3], [4]. Advances in the area of economically viable processing of high temperature ceramics using latest experimental heating techniques have focused in the fore front research area where tailoring of end product is directly possible for end use.

A number of attempts has been made to process high temperature advanced ceramics in a short time [5], [6], [7], [8], [9] to arrest and achieve suitable phase with high density sintered product. Most conventional solid-state sintering procedure of high temperature ceramics synthesis require large inter-grain diffusion of various ionic species involving a long range heating schedule. Few techniques are available to control these parameters. One of these techniques is the rapid sintering process (RSP), which produces practically dense and homogeneous bulk materials with restraint grain growth and required microstructures. Techniques of tailoring different microstructures [10], [11], [12] during processing of such ceramics for the achievements of unusual physical properties are becoming an emerging area of research in material processing and development [13], [14], [15]. Different heating sources such as microwave, laser, plasma and intermediate hybrid heating are available to tailor microstructure for achieving different physical properties within a short period as compared to conventional heating source. However, among all these techniques, the thermal plasma ones is emerging worldwide for processing of high valued advanced new materials. The major advantages of thermal plasma processing [16], [17] include a clean reaction atmosphere for high pure material production, a high enthalpy to enhance the reaction kinetics by several orders of magnitude, steep temperature gradients that provide the possibility of rapid quenching and generate fine grain particles far from equilibrium, and the ability to allow high throughput with small size installations. Some work in this area has already been reported on high temperature ceramics such as alumina, beryllia, hafnia, magnesia, silicon carbide, urania and zirconia [18], [19]. However, not much work has been reported using an extended arc thermal plasma heating (EATPH) source for processing of high temperature ceramics. We have carried out studies on sintering characteristics of Alx–Zr100−x (x=0, 10, 20, …, 100) based oxide composites materials. To our knowledge dielectric properties of this materials processed by thermal plasma heating technique has not been reported earlier. In this paper, we report the significant reduction of dielectric constant in plasma sintered Al–Zr oxide composites.

Section snippets

Experimental

A 30 kW dc power supply was used to fabricate one EATPH system. Water-cooled stainless steel double wall cylindrical chamber (outer) was fixed with suitable thermal insulation by bubble alumina for the confinement of plasma heating. Provisions were made for fine adjustment of the electrode distance to get required arc length. Plasmagen gas (argon) flow into the electrode space was provided through a narrow hole through upper electrode (cathode). Sample holder was placed coaxially between the

Results and discussion

Highly dense materials in the form of pellets were produced within 20 min of plasma sintering time. Density as a function of sintering time is presented in Fig. 1 for the plasma sintered specimens having x=30, 50 and 70. However, similar composites were sintered to identical density using 6 kW resistive furnace for 20 h in oxygen flow. It is noted that samples of desired density can be made by controlling the plasma power, sintering time and plasmagen gas flow rate. It is also noted that

Conclusion

High temperature oxide ceramics of Alx–Zr100−x (x=0, 10, 20, …, 100) composites can be sintered to high density within a few minutes using thermal plasma heating technique. This technique is very fast compared to the conventional sintering technique that normally takes a few tens of hours to sinter at elevated temperature. Dielectric constant (K) can be reduced (40% with respect to original value of the materials) drastically opting this thermal plasma heating technique within short sintering

Acknowledgements

One of the author D.R. Sahu is thankful to CSIR for his Senior Research Fellowship.

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