A Double-Side CMOS-CNT Biosensor Array With Padless Structure for Simple Bare-Die Measurements in a Medical Environment

This paper presents a double-side CMOS-carbon nanotube (CNT) sensor array for simple bare-die measurements in a medical environment based on a 0.35 $\mu{\rm m}$ standard CMOS process. This scheme allows robust measurements due to its inherent back-side rectifying diodes with a high latch-up resistance. In particular, instead of using pads, only two contact metal structures: a wide ring structure around the sensor area on the front side and a plate structure at the backside are used for both power and single I/O line. The back-side rectification is made possible by creating VDD and VSS through the back-side and front-side, respectively. The single I/O line is conditioned such that it doubles as either the power source or the ground, depending on whether the chip is face down or face up. A modified universal asynchronous receiver/transmitter (UART) serial communication scheme with pulse based I/O signal transmission is developed to reduce the power degradation during the signaling intervals. In addition, communication errors and I/O power dissipation for the receiver path are minimized by using level sensitive switch control and double sampling difference amplifier. In order to implement these special functions, a controller chip with a special I/O protocol is designed. Using this controller chip, issuing commands and receiving data can both be performed on a single line and the results are flexibly measured through either the backside or the front side of the chip contacts. As a result, a stable operation of under 150 mW maximum power at 2 MHz data rate can be achieved. The double-side chips with 32 $\times$ 32 and 64 $\times$ 64 sensor arrays occupy areas of $1.9\times 2.3 {\rm mm}^{2}$ and $3.7\times 3.9 {\rm mm}^{2}$ , respectively.