The influence of geometry and other fundamental challenges for bio-sensing with field effect transistors.

We present a review of field effect transistors (FET) from the point of view of their applications to label-free sensing in the era of genomics and proteomics. Here, rather than a collection of Bio-FET achievements, we propose an analysis of the different issues hampering the use of these devices into clinical applications. We make a particular emphasis on the influence of the sensor geometry in the phenomena of mass transport of analytes, which is a topic that has been traditionally overlooked in the analysis and design of biosensors, but that plays a central role in the achievement of low limits of detection. Other issues like the screening of charges by the ions in liquids with physiological ionic strength and the non-specific binding are also reviewed. In conclusion, we give an overview of different solutions that have been proposed to address all these challenges, demonstrating the potential of field effect transistors owing to their ease of integration with other semiconductor components for developing cost-effective, highly multiplexed sensors for next-generation medicines.

High Aspect Ratio Fin-Ion Sensitive Field Effect Transistor: Compromises toward Better Electrochemical Biosensing.

The development of next generation medicines demands more sensitive and reliable label-free sensing able to cope with increasing needs of multiplexing and shorter times to results. Field effect transistor-based biosensors emerge as one of the main possible technologies to cover the existing gap. The general trend for the sensors has been miniaturization with the expectation of improving sensitivity and response time but presenting issues with reproducibility and noise level. Here we propose a Fin-Field Effect Transistor (FinFET) with a high height to width aspect ratio for electrochemical biosensing solving the issue of nanosensors in terms of reproducibility and noise, while keeping the fast response time. We fabricated different devices and characterized their performance with their response to the pH changes that fitted to a Nernst-Poisson model. The experimental data were compared with simulations of devices with different aspect ratio, establishing an advantage in linearity and lower device resistance to provide higher current signals for the FinFETs with higher aspect ratio. In addition, these FinFETs promise the optimization of reliability and efficiency in terms of limits of detection for which the interplay of the size and geometry of the sensor with the diffusion of the analytes plays a pivotal role.

Single step fabrication of Silicon resistors on SOI substrate used as Thermistors.

Temperature sensing is one of the important features of Micro Electro Mechanical Systems and a monolithic integration provides advantages for both fabrication simplicity and performance. The use of Silicon On Insulator substrates allows simple fabrication of integrated wires that can be used as thermistors. We fabricated rectangular and triangular silicon wires with different dimensions in a single step fabrication process based on the wet etching of a <110> Silicon On Insulator substrate. We determined the experimental resistivity of the two kinds of devices and tested their performance as thermistors in a temperature range between 24 and 100 °C. The accuracy and normalized sensitivities of our devices were 0.4 °C and 0.3-0.5%/°C, respectively. The potential of the proposed method resides in the possibility of having devices with different shapes in a single straightforward process.