Both aluminum and copper are not good thin film electrode materials on which BaTiO3 can be deposited by sol gel especially. Reason being aluminum and copper will get oxidized easily at the processing temperatures normally used for processing sol gel deposited films.

Sputtered TiO2/Platinum based bilayer coatings are the best which will withstand the sol gel processing temperatures which go up to nearly 600 to 650 deg C. 

Especially for MEMS device fabrication our experience say that the processing temperature should always be less than 450 deg C.

K. Sreenivas

Thank you, sir.

I am using 0.1mm and 0.28mm thick aluminium sheet with a rectangular structure as a substrate for my device, so the device is on the centimetre scale. Will BaTiO3 reacts or gets oxidised with the same rate in macro scale too.  I am sputtering copper (~350nm) as an electrode onto an aluminium substrate, as we can not take connections on aluminium (Wire connection with soldering).

Q1. So can you please suggest me any method to overcome this problem? My structure can be in the following layer format: Al-Cu-BaTiO3-Cu (Down to up).

Q2. Or what changes should I make so that I can have proper soldering electrodes on BaTiO3 and aluminium?

At what temperatures are processing your sol gel deposited BaTiO3 film. what are the temperatures and time. This will decide which metallic substrate can be used.

commonly metals (Al, Cu, and Sn,) etc., will not do.

You need metallic electrode layers/sheets which do not oxidize of form oxide compounds, and withssand the BaTiO3 processing temperature in air, most probably like Gold  or platinum will work.

For most ferroelectric compounds you need to develop high temperature withstanding bottom electroding layers such as Pt/Ti/TiO2/SiO2/Si , which can be formed on standard silicon substrates. Thereafter your process your BaTiO3 film. Put any top electrode you like, and start back-etching you silicon substrate to form the membrane structure. All this is MEME technology and needs to be done carefully and is quite challenging.

and then try to sputter such metals on a suitable substrate which can be soldered for onward connections.

K. Sreenivas

The temperature for depositing BaTiO3 will be below 500 deg C (200,300,400 deg C for different samples) kept for 40min.

Do not have the facility to coat "Pt/Ti" at my workplace. Can only sputter (Al/Cu/Cr), spin coat (BaTiO3) and can characterise using Keithley.

Using these resources, it is not possible to form such electrodes.

Try to sputter Cr. It should protect either Cu or Al you use.