Microscale electrode array with active CMOS circuits for 2D electrochemical imaging
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Date
03/07/2019Item status
Restricted AccessEmbargo end date
03/07/2020Author
Gunasekaran, Chandrasekaran
Metadata
Abstract
Energy conversion devices make use of thin films and functional materials that exhibit
microscopic spatial heterogeneity in their efficiency. The relationship between the distribution
of such irregularities and their impact on device performance is not well understood. Hence
there is a requirement to map the electrochemical activity in a range of thin films and functional
materials. This is termed “electrochemical imaging” [1]. This need is presently addressed by
high resolution electrochemical current mapping techniques. One such approach is the use of
scanning electrochemical microscopy (SECM) [2]. While high resolution techniques like SECM
are used for imaging, they are slow (order of minutes) over a wider area (~cm² scale). Hence
there is a need to do 2D spatial electrochemical activity mapping at a faster rate (~ms) than
those obtained from the conventional techniques.
A potential solution is proposed – the CMOS active-matrix electrochemical imager – an
integrated circuit whose high-level architecture is like that of an CMOS optical imager but
whose optically sensitive element (photodiode) is replaced by an eletrochemically sensitive
element (a working electrode (WE)).
For feasibility purposes a CMOS test chip with sequential (passive matrix) readout capability
of electrode current has been designed and implemented in a 5V AMS CMOS process. It
comprises a readout circuit block (current to time converter with auto-zeroed ping-pong
amplifier) and drive circuit (potentiostat) integrated with a 3×3 array of microscale electrodes
on the same silicon substrate. The chip has been used to sense electrochemical current in the
order of nanoamperes from individual electrodes on the array. The system level architecture
to address individual electrodes, electrical characterization of individual circuit blocks, system
level electrical characterization and basic electrochemical characterization of microscale
electrodes on the 3×3 array are reported in detail.
This thesis reports in detail the design and implementation of the following standalone circuit
blocks (test structures): current amplifier, current attenuator and current buffer. The need for
the same is attributed to the wide range of steady state electrode current whose magnitude
depends on the surface area of electrode. This current can range from a few picoamperes to
hundreds of nanoamperes. The use of a current amplifier and/or current attenuator as a front
end can increase the effective input dynamic range of existing CMOS current sensing circuits.
These standalone circuit blocks were electrically tested and characterized for their current
gain with input DC currents ranging from few picoamperes to hundreds of nanoamperes.