Miniaturized portable biosensors hold significant potential for advancing sustainability and healthcare, particularly management of infectious and chronic diseases. This paper focuses on manufacturable silicon-based biosensing devices capable of detecting various analytes, including ions, proteins, and viruses, in aqueous media. Two types of electronic sensing devices are reviewed. Firstly, results for recently proposed bipolar junction (BJT) biosensors are presented. These BJT biosensor demonstrate superior sensing characteristics that are particularly well suited for applications requiring continuous monitoring with minimal human intervention. Additionally, nanoscale HfO 2 finFET biosensors designed for early diagnostics are discussed; the finFET sensors research has been licensed for commercialization rights and technology transferred to a CMOS foundry.

Shockley stated in his 1949 paper that, "The p–n–p transistor has the interesting feature of being calculable to a high degree.…" The features of bipolar transistors are calculable to a high degree because the minority-carrier current in the base flows in a single direction, from emitter to collector, enabling the formulation of analytic but mathematically simple models for the various device parameters. Shockley derived the boundary condition, the Shockley diode equation, for solving the diffusion equation governing the transport of minority carriers in the base region of a bipolar transistor. For an n–p–n transistor, this gives the local electron density, n p ( x ) in the p-type base region, which is then used to derive the equations for collector current, Early voltage, and base transit time. The n i 2 factor in the Shockley diode equation is adapted in a natural manner to account for the new physics, i.e. heavy-doping effect and base-bandgap engineering, responsible for the enhanced performance of the modern bipolar transistors.

The point-contact transistor was invented in 1947 by Bardeen and Brattain [1] , and the sandwich-like BJT was invented by Shockley in 1948 [2] . While point-contact transistors were made and used briefly for a few years, it is Shockley’s sandwich-like device structure that is commonly referred to as a bipolar transistor .

We report the first demonstration of symmetric lateral NPN transistors on SOI having epitaxially-grown emitter/collector (E/C). Employing a novel notch-assisted epitaxy scheme, using faceted Si epi as RIE mask to expose the vertical intrinsic-base epi-seeding surfaces, the epitaxial E/C are automatically connected to extension regions for metal contact and/or for electrical probing. Healthy device I-V characteristics were obtained with post-epi RTA. The results suggest a path forward for devices suitable for low-power THz electronics applications.

We report a systematic study of process-related electrical defects in symmetric lateral NPN transistors on silicon-on-insulator (SOI) fabricated using ion implantation for all the doped regions. A primary objective of this study is to see if pipe defects (emitter-collector shorts caused by locally enhanced dopant diffusion) are a show stopper for such bipolar technology. Measurements of IC-VCE and Gummel currents in parallel-connected transistor chains as a function of post-fabrication rapid thermal anneal cycles allow several process-related electrical defects to be identified. They include defective emitter-base and collector-base diodes, pipe defects, and defects associated with a dopant-deficient region in an extrinsic base adjacent its intrinsic base. There is no evidence of pipe defects being a major concern in SOI lateral bipolar transistors.

We present the first comprehensive study of symmetric lateral bipolar transistors built on Semiconductor-On-Insulator (S-OI) wafers with CMOS-like process. Record-high I C > 3 mA/μm is demonstrated. Reduced voltage operation can be achieved with small-bandgap semiconductor materials such as SiGe and Ge. Base current analysis and emitter engineering provide understanding of device physics and pathways to performance optimization. Simulation studies suggest f max > 1 THz is achievable, and BV CEO can be greatly increased in a stacked configuration.

The modulation of the currents in a symmetric Semiconductor-on-Insulator (SOI) lateral bipolar transistor with a voltage applied to the SOI substrate is studied. For an n-p-n transistor, a positive substrate bias could greatly increase the collector current, especially at low V BE values, while having relatively little effect on the base current. Similarly, a negative substrate bias could greatly increase the collector current of a p-n-p transistor. The physical mechanisms responsible for the modulation effects are discussed. The potential of using substrate bias to enhance the performance of symmetric SOI lateral bipolar circuits is briefly discussed.

The base current components in semiconductor on insulator symmetric lateral bipolar transistors are examined in detail to yield insight into the underlying device physics. For Si-OI devices, the base current component due to recombination in the quasineutral base is negligible, the component due to injection into the emitter has a weaker than 1/NE dependence because of the effect of heavy doping. The component due to recombination in the emitter-base diode space-charge region is associated with the fabrication process, and could be reduced to a negligible level with process optimization. For SiGe-OI devices, the effect of heavy doping appears to be less than for Si-OI devices. The result is higher maximum current gain for SiGe-OI devices than for comparably doped Si-OI devices.

A bipolar junction transistor (BJT) based sensor is investigated for its sensing characteristics such as sensitivity and signal to noise ratio (SNR). The sensor consists of a bipolar transistor with its base connected to a sensing surface in contact with the solution. Measurements are performed using pH buffer solutions and the sensor sensitivity and signal to noise ratio are shown to be significantly enhanced in comparison to nanowire field effect transistor (FET) sensors. In addition to the pH sensing, detection of single strand DNA is demonstrated. Lastly, the BJT sensor also provides simultaneous temperature measurement.

The reasons why state-of-the-art vertical bipolar circuits dissipate very high power are explained. The recent advent of SOI symmetric lateral bipolar transistors invites us to rethink bipolar as a high-speed but low-power technology. Integrated Injection Logic (I 2 L) and complementary bipolar (analogous to CMOS) circuits in SOI lateral bipolar offer huge design windows for power versus performance tradeoff, suggesting the possibility of ultra-low-power systems with embedded high-speed cores. I 2 L SRAM cells could be more than twice as dense as CMOS SRAM cells. The SOI substrate offers a fourth device terminal that can be used to induce narrow-gap-base HBT-like I-V characteristics, which should further improve the power-performance of circuits in SOI lateral bipolar. Fin-structure devices enable significant improvement in f max for RF and high-frequency applications. The process technology for SOI lateral bipolar is compatible with CMOS. The Si-OI version is definitely much less complex than CMOS.

We report the first demonstration of thin-base symmetric lateral NPN bipolar transistors built on 8-inch Ge-on-insulator (Ge-OI) wafers. A Ge-OI device can achieve the same collector current as a Si-OI device but at ~ 460 mV lower V BE due to the bandgap of Ge being 460 meV smaller than that of Si. Lower operation voltage should translate directly into lower power dissipation. CMOS-like process was used to fabricate lateral Ge-OI bipolar transistors. The measured collector and base currents are examined and compared with those of Si-OI and SiGe-OI devices to shed light on process-related device physics. The large observed base current at small V BE is attributed to recombination at the Ge/BOX interface in the emitter-base diode space-charge region.

We report the first demonstration of thin-base symmetric lateral NPN bipolar transistors built on 8-inch SiGe-on-insulator (SiGe-OI) wafers with CMOS-like process. Such devices achieve the same collector current as the SOI bipolar transistor at ~130 mV lower V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BE</sub> from effective bandgap lowering, translating into lower voltage operation and power dissipation. Various techniques of Emitter engineering were studied and a novel partial HBT device structure was demonstrated with 3× reduction of hole injection into the emitter.