[labnetwork] Should a pH Sensing Membrane be Conductive or Insulating?

[Mohamed Ghoneim]

When using EGFET pH sensing configuration (very similar to a metal/sensing
membrane to collect ions from solution and generate voltage).....does the
sensing thin film have to be conductive or insulating?

Example Setup:

[image: Inline image 1]

I am using EGFET setup with commercial transistor that is connected to a Au
electrode with a ZnO thin film (150 nm) on the part to be immersed in
solution to sense the pH. I also use a reference electrode to set the
offset voltage and bias the transistor.....does my ZnO thin film have to be
conductive or insulating for reliable sensor performance?

It is generally reported in literature that the preferred orientation of
ZnO used for such purposes is (002) although few reported amorphous....but
conductivity is not usually discussed. Since ZnO's conductivity is highly
tunable, it would be very helpful if its conductivity matches the
requirement for a good sensitivity and reliable measurements.


All responses and discussions are appreciated...thanks in advance,

Mohamed T. Ghoneim
<https://scholar.google.com/citations?hl=en&user=-5mNcfYAAAAJ&view_op=list_works&sortby=pubdate>
,
Postdoctoral Researcher
MIT Media Lab, Building E-15, Fourth Floor, Room 443g.
Website
<https://sites.google.com/view/mtghoneim>
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