Open-Gate Junction Field-Effect Transistor for Chemical and Biomolecular Analysis

Field-effect transistors (FETs) have emerged as a transformative platform in biosensing, effectively bridging the gap between electronics and biology by measuring the intrinsic charge of bioparticles. The development of FET-based sensing techniques can be traced back to the 1970s with the advent of the ion-sensitive FET (ISFET). This innovation stemmed from Bergveld's pioneering work on metal-oxide semiconductor-based FETs, which were modified to create ISFETs. The core innovation behind ISFETs and BioFETs was the realization that replacing the metal gate of a MOSFET-like structure with an ion-sensitive membrane could transform the device into a robust biosensor with biomolecular sensing capabilities. This modification, involving the replacement of the top gate with a solution gate, enables a sensing modality where the potential of the interface between the solution and the sensing layer (typically dielectrics) can be measured. These solid-state devices leverage the modulation of charge carriers at the semiconductor-electrolyte interface, facilitating label-free detection of biological and chemical analytes. FET biosensors offer numerous advantages, including intrinsic molecular charge sensing, real-time monitoring, high sensitivity, size scalability (ranging from a few nanometers to tens of micrometers), and compatibility with standard integrated circuit (IC) technologies such as complementary metal-oxide semiconductor (CMOS). Over the past three decades, researchers have harnessed the inherent charge sensitivity of FET sensors to detect a wide range of analytes, including ions, proteins, DNA, and other biomolecules. These sensors can selectively capture target analytes by functionalizing the FET’s gate surface with specific receptors, such as antibodies or aptamers. This capability has positioned FET biosensors as crucial tools in medical diagnostics, environmental monitoring, and drug development, driving innovation and expanding the frontiers of these fields. The widespread demand for FET sensors across diverse sensing domains underscores the critical role of standard foundry-based fabrication methodologies. Efforts to refine FET sensor fabrication processes for enhanced reliability, scalability, and reproducibility are crucial for mass production and widespread adoption. Standard foundry-based fabrication techniques ensure uniformity and consistency in device performance, enabling seamless integration into diverse sensing platforms across industries. Most standard FET sensors (or ion-sensitive FETs) have been realized by CMOS platforms, which allow these sensors to be manufactured in an almost flawless foundry process that creates ICs in our cell phones. Various CMOS-based ISFET configurations were made and used for different biosensing applications. Later, graphene and carbonaceous materials were used as novel high-performance FET biosensors. However, the real breakthrough came with the efforts to standardize graphene FETs through foundry fabrication, pioneered by companies such as Cardea Bio and Graphena. This strategic initiative has not just made graphene FETs more accessible but has democratized access to them, previously hindered by prohibitive costs. This development fosters accessibility for researchers and industrial stakeholders, opening new avenues for research and innovation. By leveraging standard foundry-based fabrication approaches, FET sensors are poised to meet the escalating demand for reliable, high-performance sensing solutions. This advancement could catalyze innovation across various fields, spanning healthcare, environmental monitoring, agriculture, and beyond. The recent introduction of the open-gate junction field-effect transistor (OG-JFET) by CMC Microsystem represents a significant advancement in silicon-foundry-based FET sensor technology standardization. The OG-JFET foundry enables the mass production of chips with diverse designs on a silicon wafer, allowing for customized configurations tailored to specific application requirements. The structural innovation of the OG-JFET, achieved by removing the top gate of a p-type JFET sensor and introducing a soft material, indicates a new era of charge-sensing capabilities within a JFET electronic structure. Understanding the intricate physics of the charge sensing mechanism and its integration with microfluidics has been pivotal in unlocking the full potential of the OG-JFET. As the technology is still in its early stages of development and scale-up, user-friendly CAD tools and dedicated portable characterization systems have emerged as a cornerstone for successful adoption and integration in academic and industrial research settings. This system enhances performance and facilitates seamless integration into diverse research environments. This thesis is dedicated to tackling the challenges inherent in comprehending the charge-sensing physics of OG-JFET sensors and exploring the design and simulation of these sensors to discern the impacts of various design parameters. At the heart of this research lies developing a portable characterization system and electro-fluidics packaging schemes to streamline testing and characterization processes. A key objective of this endeavor is to standardize these processes, thereby overcoming the barrier posed by the high cost and limited accessibility of conventional characterization equipment such as probe stations and semiconductor analyzers. By providing researchers with accessible and cost-effective alternatives, this research seeks to democratize access to this FET sensor foundry technology, thus fostering innovation and discovery in chemical and biological sensing. These concerted efforts aim to accelerate the adoption and advancement of FET sensor technology, paving the way for transformative breakthroughs in scientific inquiry and technological applications.