Oxides!

12 11 2010

It’s been chaos round here lately and so this is the first post for a while. I’m busy trying to write an application to the EPSRC Basic Technology Call, which closes on the 24th of November, as well as decide on my research strategy for the next five years. There’s also a lot of interest in the call from the UK Space Agency about putting small payloads on a small satellite, UKube, planned for launch in December 2011. We’re looking to bid to get some of our stuff onboard, but the deadline is the same day as the EPSRC bid. The next opportunity in the mix, is an advert for the next silicon carbide conference, in June next year. The WASMPE/Hetero-Sic conference is going to be held in Tours, which sounds really nice, in June 2011. The best bit, is that you can get there on the train, and avoid all the hassle of airports.

During all this, the JFETs have been in further testing and we now have some 800 functional devices, some of which have gate leakage below 100pA. They are now being diced out before we get them packaged up for long term testing and circuit construction. At the same time, Ben’s gas sensors have now been characterised (at room temperature) and are also off to be diced at the Scottish Microelectronics Centre.

So, during all this, Ben has characterised literally hundreds of capacitors, which are the fundamental component of our gas sensors. These comprise a high K dielectric (oxide) layer stack on the SiC and so a lot of his work has been to understand how the oxide layer functions.

Raman characterisation of the dielectric layers has shown evidence of what appears be rutile phase TiO2 and amorphous HfO2. This would tie in well with the observation that the leakage current is generally higher in the TiO2 samples, as might be expected from grain boundary leakage. The TiO2 samples also show a higher dielectric constant, which could in part be linked to the crystalline nature.

dielectric raman data TiO2 HfO2

Raman data on high K dielectrics

However, phase contrast AFM data seems to suggest that the dielectrics are crystalline in nature. The data also shows that the catalytic contacts follow the topology of the underlying dielectric, with a similar grain size.

AFM phase contrast topology high K dielectrics

AFM Images of capacitor strucures

So, at this stage the jury is out on the behaviour of our dielectrics and how this is related to the material properties. Next stage is to watch the grain evolution with temperature, as these sensors often require substantial activation anneals prior to use and then it’s off to the test cell on the roof. I hate to mention this to Ben, but the heating up there doesn’t work and I think January / February up there could be more than a bit cold …

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