System Bits: May 23

Diamond transistors; switchable transistors; graphene kills bacteria.


Next-era transistors engage diamonds
To advance the development of more robust and energy-efficient electronics, materials scientists from Japan’s National Institute for Materials Sciences have developed a new diamond transistor fabrication process.

To address the challenges of silicon, Jiangwei Liu and the team have recently described new work developing diamond-based transistors. “Silicon-based transistors often suffer from high switching loss during power transmission and fail when exposed to extremely high temperatures or levels of radiation. Given the importance of developing devices that use less power and perform under harsh conditions, there has been a lot of interest within the broader scientific community in determining a way to build transistors that utilizes manufactured diamonds, which are a very durable material.” 

With this in mind, the team developed a new fabrication process involving diamond, bringing “hardened electronics” closer to realization.     

Yasuo Koide, a professor and senior scientist at the National Institute for Materials Science leading the research group said, “Manufactured diamonds have a number of physical properties that make them very interesting to researchers working with transistors. Not only are they physically hard materials, they also conduct heat well which means that they can cope with high levels of power and operate in hotter temperatures. In addition, they can endure larger voltages than existing semiconductor materials before breaking down.” 

The research group said they focused their work on enhancement-mode metal-oxide-semiconductor field-effect transistors (MOSFETs), a type of transistor that is commonly used in electronics, and that one of the developments that makes the fabrication process innovative is that yttrium oxide (Y2O3) insulator was deposited directly onto the surface of the diamond [to form the gate]. The yttrium oxide was added to the diamond with a technique known as electron beam evaporation, which involves using a beam of electrons to transform molecules of yttrium oxide from the solid state to the gaseous state so that they can be made to cover a surface and solidify on it. This has many desirable qualities, including high thermal stability, strong affinity to oxygen and wide band gap energy, which contributes to its capabilities as an insulator.

Going forward, the team hopes to refine their understanding of electron movement through the diamond transistor with future research projects, and ultimately to build integrated circuits with diamonds.

Transistors that can switch between two stable energy states
In a development that could be used to boost computer processor speeds, University of Illinois researchers have unveiled an upgrade to the transistor laser to allow the formation of two stable energy states and the ability to switch between them quickly. 

The team reminded that modern computers are limited by a delay formed as electrons travel through the tiny wires and switches on a computer chip, and to overcome this electronic backlog, engineers would like to develop a computer that transmits information using light, in addition to electricity, because light travels faster than electricity.

Further, having two stable energy states, or bistability, within a transistor allows the device to form an optical-electric switch. That switch will work as the primary building block for development of optical logic – the language needed for future optical computer processors to communicate, explained Milton Feng, the Nick Holonyak Jr. Emeritus Chair in electrical and computer engineering at the University of Illinois.

“Building a transistor with electrical and optical bistability into a computer chip will significantly increase processing speeds because the devices can communicate without the interference that occurs when limited to electron-only transistors,” Feng continued.

University of Illinois engineer Milton Feng and his team have introduced an upgrade to transistor lasers that could boost computer processor speeds. (Source: University of Illinois)

The researcher team has now described how optical and electrical bistable outputs are constructed from a single transistor. The addition of an optical element creates a feedback loop using a process called electron tunneling that controls the transmission of light.

Feng said the obvious solution to solving the bottleneck formed by big data transfer – eliminating the electronic data transmission of the transistor and use all optics – is unlikely to happen. “You cannot remove electronics entirely because you need to plug into a current and convert that into light. That’s the problem with the all-optical computer concept some people talk about. It just is not possible because there is no such thing as an all-optical system.”

Graphene — bad news for bacteria
Rice University and Ben-Gurion University of the Negev (BGU) researchers have discovered that laser-induced graphene (LIG) is a highly effective anti-fouling material and, when electrified, bacteria zapper.

LIG is a spongy version of graphene, the single-atom layer of carbon atoms. The Rice lab of chemist James Tour developed it three years ago by burning partway through an inexpensive polyimide sheet with a laser, which turned the surface into a lattice of interconnected graphene sheets. The researchers have since suggested uses for the material in wearable electronics and fuel cells and for superhydrophobic or superhydrophilic surfaces.

According to their report in the American Chemical Society’s ACS Applied Materials and Interfaces, LIG also protects surfaces from biofouling, the buildup of microorganisms, plants or other biological material on wet surfaces.

In the top row, the growth of biofilm on surfaces with a solution containing Pseudomonas aeruginosa is observed on, from left, polyimide, graphite and laser-induced graphene surfaces. Green, red and blue represent live bacteria, dead bacteria and extracellular polymeric substances, respectively. At bottom, a sheet of polyimide burned on the left to leave laser-induced graphene shows the graphene surface nearly free of growth. (Source: Rice University)

“This form of graphene is extremely resistant to biofilm formation, which has promise for places like water-treatment plants, oil-drilling operations, hospitals and ocean applications like underwater pipes that are sensitive to fouling, The antibacterial qualities when electricity is applied is a great additional benefit,” Tour said.

According to the team, when used as electrodes with a small applied voltage, LIG becomes the bacterial equivalent of a backyard bug zapper. Tests without the charge confirmed what has long been known — that graphene-based nanoparticles have antibacterial properties. When 1.1 to 2.5 volts were applied, the highly conductive LIG electrodes “greatly enhanced” those properties.

Under the microscope, the researchers watched as fluorescently tagged Pseudomonas aeruginosa bacteria in a solution with LIG electrodes above 1.1 volts were drawn toward the anode. Above 1.5 volts, the cells began to disappear and vanished completely within 30 seconds. At 2.5 volts, bacteria disappeared almost completely from the surface after one second.

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