Towards direct biochemical analysis with weak inversion ISFETs

A weak inversion region is shown to exist in ISFET sensors. It is therefore proposed that the ISFET and its ChemFET and EnFET counterparts be used as translinear elements in the synthesis of novel biochemical input stages which perform real-time mathematical manipulation of biochemical signals. A biochemical translinear principle using weakly-inverted ChemFETs is presented. The first order temperature dependence of biochemical translinear circuits is greatly reduced from that of voltage-mode circuits. A low-power current-mode input stage circuit is presented as an application of the principle. This yields a linear relation between drain current and hydrogen ion concentration valid over 4 decades. This paper demonstrates an important and necessary step towards biochemical VLSI.