Characterization of an ISFET with Built-in Calibration Registers through Segmented Eight-Bit Binary Search in Three-Point Algorithm Using FPGA

Sensors play the most important role in observing changes in an environment they are a part. They detect even the smallest changes and send the information to other electronic devices. Making sure that these sensors provide an accurate output is equally crucial, as the data it measures and collects are used for analysis. Until now, calibrating sensors has been done manually by following a sequence of procedures, and is usually performed on-site or in a laboratory prior to deployment. To eliminate the manual procedure in the calibration (at the very least), an ion-sensitive field-effect transistor (ISFET) with a built-in calibration registers circuit was created through segmented eight-bit binary search in a three-point algorithm using a field-programmable gate array (FPGA). The circuit was created using a three-point calibration algorithm and three standard buffers (pH 4, pH 7, and pH 10). The block diagram, schematic diagram, and the number of logic gates were derived after synthesizing the Verilog program in Xilinx/FPGA. An average of 0.30% error was computed to prove the reliability of the created circuit using FPGA. Having an ISFET with built-in calibration registers will alleviate the work of experts in performing calibrations. This would follow the plug and play standard, hence its being a calibration-ready ISFET device. With this feature, it could be used as a pH level meter or a remote sensor node in several applications

Production and electrical characterization of microsensors for marine mutagens and carcinogens monitoring

Field effect-based devices (FED) show several advantages when implemented as biosensors, such as small dimensions, fast response, low-cost mass production and easy integration with CMOS or TFT technol- ogies. However, conventional architectures have some inherent drawbacks that hinder further miniaturisation. Recently, a charge-modulated field-effect transistor (CMFET) architecture has been developed, following the operation principle of the floating-gate transistor, used in memory devices, having a control-gate functioning as reference electrode and a sensing area activated by charge induction, which modulates the channel of an integrated MOS transistor. This work focuses on the development and optimization of CMFET sensor archi- tecture produced for the first time on eco-friendly and flexible paper substrates. The performance of these paper based CMFETS was then compared with the previously developed sensors produced on substrates such as Corning glass and polyethylene naphthalate (PEN), which shared an identical fabrication process already established at CENIMAT|I3N. Measurement and analysis protocols were created and optimized to assess the sensors’ performance and establish a comprehensive comparison between sensors fabricated on different sub- strates. Furthermore, an alternative connecting topology was tested for the developed charge-modulated field- effect sensing architecture, with results of sensitivity scaling up to 300% relative to the values obtained with the standard connecting topology, identical to the ones reported in the literature. Although it was not possible to attain a batch of devices without considerable variability in capacitance, sensors on paper substrates were capable of outputting distinct current levels for each pH buffer solution tested (7, 4 and 10) exhibiting a sen- sitivity of 14 ± 2 mV/pH (Whatman paper) and 32 ± 6 mV/pH (CelSmartSense paper), relative to 33 ± 3 mV/pH obtained for sensors produced on Corning glass and 28 ± 2 mV/pH for sensors on PEN substrate, improving the sensitivity and signal to noise ratio previously reported for this architecture.Dispositivos baseados em efeito de campo (FED) apresentam inúmeras vantagens quando implemen- tados como biossensores, entre as quais, reduzidas dimensões, resposta rápida, produção em massa de baixo custo e fácil integração com tecnologias CMOS ou TFT. No entanto, as arquiteturas mais comuns apresentam algumas desvantagens que criam uma barreira ao processo de miniaturização. Recentemente foi desenvolvida uma arquitetura sensorial baseada em modulação de cargas por efeito de campo (CMFET), que segue o prin- cípio de operação do transístor de porta flutuante, utilizado em dispositivos de memória, fazendo uso de um elétrodo de controlo e uma área sensível ativada por indução de cargas, que modula o canal de condução de um transístor MOS integrado. Este trabalho foca o desenvolvimento e caracterização elétrica de sensores ba- seados na arquitetura CMFET em substratos de papel ecológicos e flexíveis. A performance destes sensores foi por sua vez comparada com sensores fabricados substratos de referência como vidro Corning e naftalato de polietileno (PEN), que partilharam um processo de fabricação idêntico, já estabelecido no CENIMAT|I3N. Protocolos de medição e análise foram criados e otimizados para comparar o desempenho dos sensores fabri- cados em diferentes substratos. Além disto, um esquema de conexão alternativo foi testado para esta arquite- tura de sensores, exibindo resultados de sensibilidade que escalaram 300% face a resultados testados com a conexão standard, idênticos aos reportados na literatura. Embora não tenha sido possível produzir lotes de dispositivos sem uma variabilidade considerável na sua capacitância, os sensores fabricados foram capazes de produzir níveis de corrente distintos para cada pH testado (4,7 e 10), exibindo uma sensibilidade de 14 ± 2 mV/pH (papel Whatman) e 32 ± 6 mV/pH (papel CelSmartSense), em relação a 33 ± 3 mV/pH, valor obtido com sensores produzidos em vidro corning e 28 ± 2 mV/pH para sensores produzidos em substrato de PEN, melhorando a sensibilidade conseguida anteriormente com esta arquitetura