Power/Performance Bits: Oct. 28

More powerful, sensitive wearables
With their special electronic and optical properties, nanomaterials such as graphene and molybdenum sulfide have created excitement among UCLA scientists for their potential to revolutionize transistors and circuits.

Research is underway there that has the potential to increase the efficiency and capabilities of the 2D layered semiconductors used in high-speed, flexible electronic devices. The drawback is that graphene’s structure lacks a feature called a band gap, which allows current through the material to be turned on and off. However, unlike graphene, molybdenum sulfide has a band gap and can function as an atomically thin semiconductor and allow atomically thin transistors with high on-off ratios and high voltage gain.

The UCLA team has created field effect transistors made from molybdenum sulfide that demonstrated the best performance to date in a transistor of this type, and they expect this could mean vastly more powerful and sensitive fitness and health trackers, smartphones, computer-interface eyewear and other wearable applications.

The transistor developed at UCLA could mean vastly more powerful and sensitive wearable devices. (Source: UCLA)

The scientists found that electronic devices such as logic inverters or radio frequency amplifiers can be formed by integrating multiple molybdenum sulfide transistors on quartz or flexible plastic substrates with voltage gain in the gigahertz regime. They said transistors they produced had a cut-off frequency of up to 42 gigahertz and a maximum oscillation frequency up to 50 gigahertz. Existing transistors have achieved readings of 0.9 gigahertz and 1 gigahertz, respectively.

Ferroelectrics may replace transistors
According to a team of researchers at UC Berkeley and the University of Pennsylvania, ferroelectric materials, which are commonly used in transit cards, gas grill igniters, video game memory among other things, could become strong candidates for use in next-generation computers.

The researchers report that they’ve found an easy way to improve the performance of ferroelectric materials in a way that makes them viable candidates for low-power computing and electronics.

Specifically, ferroelectric materials have spontaneous polarization as a result of small shifts of negative and positive charges within the material. A key characteristic of these materials is that the polarization can be reversed in response to an electric field, enabling the creation of a “0” or “1” data bit for memory applications. Ferroelectrics can also produce an electric charge in response to physical force, such as being pressed, squeezed or stretched, which is why they are found in applications such as push-button igniters on portable gas grills. The researchers discovered a fundamentally new and unexpected way for these ferroelectric materials to respond to applied electric fields, and they believe it opens up the possibility for faster switching and new control over novel, never-before-expected multi-state devices.

The herringbone pattern of nanoscale domains is key to enabling faster switching in ferroelectric materials. For scale, each tiny domain is only about 40 nanometers wide, or roughly 1/2500 the width of an average human hair. Each colored band is made up of many tiny domains. (Source: UC Berkeley)