I've been looking for this information but didn't find any clear answers. I've been told by many that I should opt for FTO glass for my experiments (thin film deposition) since I need thermal treatments beyond 400 °C, because ITO would degrade. I would be grateful if someone can direct me towards reliable source to confirm if typical commercial ITO glass would be unstable at these temperatures. Thanks
The softening of your glass substrate is the key factor here. In the past ITO coated 7740 (borosilicate) was available in addition to normal soda-lime float glass coated glass. I saw no evidence in the 1980's while making LCD's that there was any degradation of bought-in ITO substrates with heating up to 425 C. However, under conditions of 85 C and 95% humidity, then, over a period of time, leaching of sodium from conventional soda lime glass would be a problem and a silica barrier layer under the ITO was needed to slow down this process which leads to device failure over a period of a few weeks. BTW, the borosilicate glass was harder to scribe reliably but it was entertaining to bond one plate of this to a soda lime piece. The different coefficients of expansion led to curved plates which (of course) could not be processed into devices,
I agree with Alan F Rawle that the substrate stability will be crucial factor.
You may also find the following article useful:
Article Investigation of temperature stability of ITO films characteristics
Dear Victor,
The post heat treatment can affect reversible changes in the structural properties of the ITO and the other thin films. The major structural changes is the conversion of the film from amorphous to poly crystalline form and further growth of the grains. This leads to changes in the physical properties of the material including the optical and electrical properties.
I would like that you see the paper in the link:Article The effect of annealing treatment on microstructure and prop...
You will get quantitative answer on your question.
Best wishes
In my experience, you can heat up to 650 C for 6 hours, after that, it may be converted into soft and melting state. It adopts the state, in which it has been placed like crucible etc. Thank you.
Hi Victor,
FTO can sustain its optical property up to 600oC and for ITO is up to 400oC in the ambient. For the thermal treatment of the sputtered ITO thin film, you can keep the film at 400 oC within 1hour, beyond 400oC, its optical property starts to degrade.
Regards,
Thang
Thank you all for your replies.
FYI, I made the experiment, and our ITO's optical and conducting properties got affected at temperatures as low as 300-350 °C
Victor Malgras That’s good to know - thanks for reporting back. Was this ordinary soda-lime glass? Barrier layer?
Alan F Rawle yes ordinary soda-lime, no additional barrier (from what I understood). Discussing with some experts in solar cells research, ITO is never used if further thermal treatment beyond 250°C are necessary.
I would like to draw the attention towards this link which states that ITO is thermally stable only up to 350°C while FTO is stable upto 600°C. Since the link itself belongs to a vendor, I could believe it being true and trustworthy.
https://www.techinstro.com/difference-ito-fto-coated-glass/#targetText=TCO%20such%20as%20Indium%20tin,and%20FTO%20coated%20glass%20used.
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