Attoampere CMOS Current-Sensitive Preamplifier with Leakage-Free Reset Network

In this paper, we propose a CMOS current front-end capable of resolving attoamperes with an averaging time of few seconds. The key component that allows this sensitivity is a reset network based on tunneling and/or hot-electron injection that introduces virtually no leakage (< 1 aA) and no noise (< 20 aA / √Hz) when not activated, unlocking the full potential of a capacitive transimpedance amplifier as a current front-end. To preserve the attoampere resolution in operative conditions against the presence of leakages that might degrade the reading, surface passivation of the chip by means of hexamethyldisilazane is demonstrated to reduce surface conductivity by three orders of magnitude and reduce leakage currents to few aA, thus allowing tracking on very long experiments before saturation occurring. Finally, the configuration results in a signal-to-noise ratio that improves linearly with averaging time (T_avg), as opposed to sptandard systems where the improvement is proportional to √T_avg, further enhancing the performance of the system with a limited additional time extension. The proposed current detection front-end may therefore prove very useful in all fields where extremely high current resolution is required, such as in nanoelectrochemistry, molecular electronics or spin-polarized photoelectron spectroscopy.