Synthesis and characterization of polyvinylpyrrolidine assisted tantalum pentoxide films

Micron thick tantalum pentoxide (Ta₂O₅) films have been proposed as thermal insulating layers in microchemical systems, but so far it has been difficult to deposit thick enough films over complex substrates. So far sol-gel films cracked upon heating whenever the film thicknesses were above 350 nm. A 350 nm thick film is too thin for effective insulation. Other techniques are not suitable for coating the complex structures associated with microchemical systems. In this paper we report sol-gel synthesis of 1.6 μm thick tantalum pentoxide (Ta₂O₅) films. The films are almost crack free, and adhere to silicon surfaces even upon flashing to 900 °C. The key to the synthesis is the addition of Polyvinylpyrrolidine (PVP) to the sol. Films grown in the absence of PVP all show cracks upon calcination to 900 °C while few cracks are seen with PVP. X-ray diffraction and Fourier transform infra red analysis show that orthorhombic Ta₂O₅ is formed in all cases. X-ray photoelectron spectroscopy shows the O:Ta ratio to be 2.8:1. This shows that sol-gel is a viable process for making the micron thick films of Ta₂O₅ needed as insulators for microchemical systems.