Researchers report wafer-scale fabrication of CMOS-integrated graphene-field effect transistor (GFET) arrays with extremely high yield and uniformity. This achievement is of high importance for a number of applications, including biosensing, gas and chemical sensing, and infrared imaging. The findings were published in the journal ACS Applied Electronic Materials.

Image: (Left) A CMOS-integrated GFET chip bonded to a chip carrier. (Right) Electrical measurement configuration of the GFETs. Source: Soikkeli et al, ACS Appl. Electron. Mater. 2023.

The researchers from VTT Technical Research Centre of Finland and Graphenea utilized a process that results in a CMOS readout circuit with embedded graphene devices. The complex fabrication process, that is compatible with complementary metal-oxide semiconductor (CMOS) technology that is today’s standard in semiconductor fabrication, makes use of Graphenea graphene, with a final yield of 99.9%, with 2558 devices working out of a measured 2560 devices across 5 microchips. Furthermore, the uniformity of the process is high, with very little resistance variation between devices and chips.

Image: (Left) A photograph of GFETs on top of the CMOS readout circuit. (Right) Schematic crosscut of the GFETs on CMOS readout. Source: Soikkeli et al, ACS Appl. Electron. Mater. 2023.

To demonstrate sensing performance, the devices were used to detect the concentration of sodium chloride in a buffer solution. Sodium chloride detection exhibited high stability and repeatability, with an average sensitivity of 42 mV/dec in the range 1 to 100 mM. The demonstration is just a proof-of-concept to show the reliability of the method, with anticipated use in specific biomolecule detection, such as in point-of-care diagnostics situations.

The employed fabrication strategy will play a pivotal role in the commercialization of biosensors based on GFETs. It will facilitate the capability of detecting multiple analytes and performing the necessary statistical evaluations for precise on-chip biological assays. Looking ahead, this on-chip multianalyte sensing approach has the potential to streamline the screening process for numerous viruses. This could provide robust detection from a tiny analyte sample, backed by substantial statistical data.

The described technology facilitates the utilization of GFET channels in various sizes, accommodating a potential range of GFET numbers spanning from thousands to millions of devices. This variability is contingent on the design and technology of the ASIC circuit. Such adaptability concerning device quantity and size opens the door to a broader array of applications. This is particularly advantageous in scenarios where substantial volumes of biological data must undergo assessment, including fields like gene sequencing.

The most common issues in the development of FET-based biosensing are related to the reliability and repeatability of individual devices and analysis. In many cases, the sensor chips are only used in a single measurement; hence, individual faulty devices, voids in the functionalization, and small air bubbles can lead to misinterpretation of results. The large-scale statistics provided by CMOS multiplexed sensor arrays on a single chip will improve the general reliability of the analysis and enable easy removal of defective devices from the data.

The showcased technology further unlocks opportunities for producing gas sensor arrays and infrared cameras integrated with CMOS technology on a wafer-scale, as previously showcased. In this context, the advancement of GFETs as a versatile foundation that can be tailored based on functionalization choices paves the way for applying this technology across diverse applications.