Transistors

Researchers from the University of Göttingen, Japan's National Institute for Materials Science and Massachusetts Institute of Technology (MIT) have demonstrated experimentally that electrons in naturally occurring double-layer graphene move like particles without any mass, in the same way that light travels. Furthermore, they have shown that the current can be "switched" on and off, which has potential for developing tiny, energy-efficient transistors. 

Among its many unusual properties, graphene is known for its extraordinarily high electrical conductivity due to the high and constant velocity of electrons travelling through this material. This unique feature has made scientists try to use graphene for faster and more energy-efficient transistors. The challenge has been that to make a transistor, the material needs to be controlled to have a highly insulating state in addition to its highly conductive state. In graphene, however, such a "switch" in the speed of the carrier cannot be easily achieved. In fact, graphene usually has no insulating state, which has limited graphene's potential a transistor.

Archer Materials has designed a miniaturized version of its Biochip graphene field effect transistor ("gFET") chip for fabrication at a commercial foundry.

The Archer Biochip contains a sensing region of which the gFET is the core component. Each gFET chip contains multiple gFETs, each of which is a transistor, which acts as a sensor. Archer has miniaturized the total chip size by redesigning the layout of the circuits creating these gFET transistors. The new miniaturized design has been sent to a foundry partner for a whole-wafer fabrication of reduced size gFET chips, which Archer intends to integrate with other parts of the Biochip technology.

Traditional microelectronic architectures are currently used to power everything from advanced computers to everyday devices. However, scientists are always on the lookout for better technologies. Recently, Los Alamos National Laboratory scientists and their collaborators from Menlo Systems and Sandia National Laboratories, have designed and fabricated asymmetric, nano-sized gold structures on an atomically thin layer of graphene. The gold structures are dubbed “nanoantennas” based on the way they capture and focus light waves, forming optical “hot spots” that excite the electrons within the graphene. Only the graphene electrons very near the hot spots are excited, with the rest of the graphene remaining much less excited.

Illustration of an optoelectronic metasurface consisting of symmetry-broken gold nanoantennas on graphene. Image from Nature

The team adopted a teardrop shape of gold nanoantennas, where the breaking of inversion symmetry defines a directionality along the structure. The hot spots are located only at the sharp tips of the nanoantennas, leading to a pathway on which the excited hot electrons flow with net directionality — a charge current, controllable and tunable at the nanometer scale by exciting different combinations of hot spots. 

Researchers at Northwestern University, MIT, Harvard University, CIFAR Azrieli Global Scholars Program and Japan's National Institute for Materials Science have developed a graphene-based synaptic transistor capable of higher-level thinking.

The device simultaneously processes and stores information just like the human brain. In new experiments, the researchers demonstrated that the transistor goes beyond simple machine-learning tasks to categorize data and is capable of performing associative learning.

An international team of researchers, including scientists from University of California San Diego, Chinese Academy of Sciences, University of Texas Medical Branch and University of Illinois Urbana-Champaign, has developed a handheld, non-invasive graphene-based device that can detect biomarkers for Alzheimer’s and Parkinson’s Diseases. The biosensor can also transmit the results wirelessly to a laptop or smartphone.

The biosensor consists of a chip with a highly sensitive transistor, made of a graphene layer that is a single atom thick and three electrodes–source and drain electrodes, connected to the positive and negative poles of a battery, to flow electric current, and a gate electrode to control the amount of current flow. Image credit: UCSD

The team tested the device on in vitro samples from patients. The tests reportedly showed the device is as accurate as other state-of-the-art devices. Ultimately, researchers plan to test saliva and urine samples with the biosensor. The device could be modified to detect biomarkers for other conditions as well.

Archer Materials, a semiconductor company advancing the quantum computing and medical diagnostics industries, has demonstrated multiplexing readout for its advanced Biochip graphene field effect transistor (“gFET”) device.

Archer confirmed single-device multiplexing using four advanced gFETs as sensors, which were integrated into the Archer advanced Biochip platform. This is significant as Archer intends to apply its multiplexing capability in the Biochip to test for multiple diseases on a single chip at once.

Researchers at Graphenea, University of Utah and Kairos Sensors have examined a perovskite-based graphene field effect transistor (P-GFET) device for X-ray detection. 

The device architecture consisted of a commercially available GFET-S20 chip, produced by Graphenea, with a layer of methylammonium lead iodide (MAPbI₃) perovskite spin coated onto the top of it. This device was exposed to the field of a molybdenum target X-ray tube with beam settings between 20 and 60 kVp (X-ray tube voltage) and 30–300 μA (X-ray tube current). Dose measurements were taken with an ion-chamber and thermo-luminescent dosimeters and used to determine the sensitivity of the device as a function of the X-ray tube voltage and current, as well as source-drain voltage. 

A research team from the University of Illinois Urbana-Champaign and the University of California has reported that the friction on a graphene surface can be dynamically tuned using external electric fields. 

The team studied the friction at a single asperity nanoscale contact between the graphene surface of graphene FETs and an AFM tip in a dry nitrogen atmosphere, while the doping level of graphene was modulated in situ by changing the potential applied to the device’s back gate. In contrast to conducting or insulating contacts, graphene in contact with semiconducting tips exhibits an enhanced and tunable friction sensitive to the charge density in graphene.

Archer Materials has had its advanced graphene field effect transistor (“gFET”) chip design validated by a commercial foundry partner in the Netherlands with a whole four-inch wafer run.
 

The new advanced gFET device designs have been fabricated and the whole wafer run foundry process was reportedly successful. The electronic and spectroscopic characteristics of the gFET chips, and the foundry fabrication process yield, are said to be consistent with what Archer expected. The gFET chips are also compatible with Archer’s biochip system platform.

A team of researchers, led by the University of Wisconsin-Milwaukee, recently developed a path to mass-manufacture high-performance graphene sensors that can detect heavy metals and bacteria in flowing tap water. This advance could bring down the cost of such sensors to just US $1 each, allowing people to test their drinking water for toxins at home.

The sensors have to be extraordinarily sensitive to catch the minute concentrations of toxins that can cause harm. For example, the U.S. Food and Drug Administration states that bottled water must have a lead concentration of no more than 5 parts per billion. Today, detecting parts-per-billion or even parts-per-trillion concentrations of heavy metals, bacteria, and other toxins is only possible by analyzing water samples in the laboratory, says Junhong Chen, a professor of molecular engineering at the University of Chicago and the lead water strategist at Argonne National Laboratory. But his group has developed a sensor with a graphene field-effect transistor (FET) that can detect toxins at those low levels within seconds.