Here we present the design, fabrication and characterization of a

Here we present the design, fabrication and characterization of a single chip wireless chemical sensor based on a commercial 0.35 ��m CMOS technology. The focus of our approach has been to keep the post-processing simple, with no additional deposition or lithography steps. The chip includes two types of impedimetric transducers, a 4-electrode array and a pair of interdigitated electrodes, for the implementation of chemical sensors. Impedimetric transducers are easy to integrate because they do not require a reference electrode, unlike potentiometric or amperometric ones. By measurement of changes in conductivity or permittivity of a solution, this transducers have been used to acquire chemical parameters, like pCO2 [7], ethanol content in fuel [8], and hematocrit [9].

Biosensors have been obtained by combining impedimetric transducers with enzymes [10�C12], and antibodies [13,14]. They have also Inhibitors,Modulators,Libraries been combined with selective membranes for the detection of ions such us calcium [15] and pH [16]. Therefore, the integration of impedimetric transducers with their associated instrumentation, inductive powering, and data transmission circuits will enable the development of a wide variety of single-chip, wafer-level encapsulated wireless chemical sensors.2.?Design and FabricationThe block diagram of the system is depicted in Figure 1a. The external readout unit transfers power and control data to the chip by inductive telemetry, that is, by generating an alternating magnetic field with a loop antenna, which in turn produces an alternating electromotive force at the integrated coil.

The received voltage is rectified and regulated to generate a stable voltage supply for the integrated circuits. Inhibitors,Modulators,Libraries The impedimetric transducers are excited and measured with analog signal processing circuits, and the resulting impedance value is converted Inhibitors,Modulators,Libraries to the digital domain with a simple Pulse Width Modulation technique and transmitted back to the readout unit by load modulation. The process of measurement and data transmission is controlled Inhibitors,Modulators,Libraries by a digital Brefeldin_A block. The data to program the digital block is transferred from the external readout unit by amplitude modulation of the power signal.Figure 1.(a) Block diagram of the wireless chemical sensor measuring in the solution of a sealed container. (b) Distribution of blocks and components on the actual chip design (represented as the superposition of fabrication masks).

The 3.5 �� 3.5 mm chip (Figure 1b) containing all the blocks and components shown in Figure 1a diagram was fabricated with a commercial CMOS technology (AMS035HV4M, Austria Microsystems) and post-processed in our laboratory. Various blocks and components scientific research of the system were made accessible through connection pads to allow their individual characterization.2.1. Impedimetric transducersThe electrodes for the impedimetric transducers have been formed in polycrystalline silicon (polysilicon).

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