By Dr.SS Verma, Professor, Department of Physics, SLIET
Electronic devices
Electronic devices becoming the modern life style have put a great pressure on the conventional sources of energy and thus need to be energy efficient for sustainable growth. Electronics such as TVs, desktop computers and monitors can be huge energy users. Consumer electronics represents 15% of worldwide home power demand. Without major changes, that percentage is expected to triple by 2030. We need electronics which either require no energy or very little energy for its operation/use. Nanotechnology is expected to play a great role in this direction as nanotechnology can be used to help cool electrons with no external sources. Dissipating heat from electronic devices is important, because the devices become unreliable when they become too hot. Reducing
electricity consumption in electronic devices, thus, saving energy, money, and environment is the motto with growing use of electronic devices. Researchers are looking for new methods of reducing the power consumption in electronic devices. Lower power consumption offers lower electricity bills and a reduced carbon footprint, with less harmful emissions of greenhouse gases. Many electronic devices are designed to be put into a “standby” mode rather than switched off completely. Although the power used in standby may be relatively low, the 24×7 usages can result in significant total power consumption over time. The standby power page provides advice on how to assess standby power levels and ways to reduce or eliminate it. The good news is that the latest and best technology is also ultra energy efficient. When shopping for a new electronic product one should select that are among the best made today—and that are also at least 30% more energy efficient than the basic specification.
Role of nanotechnology
Nanotechnology is already in use in many computing, communications, and other electronics applications to provide faster, smaller, and more portable systems that can manage and store larger and larger amounts of information. Nanoelectronics refer to the use of nanotechnology in electronic components. The term covers a diverse set of devices and materials, with the common characteristic that they are so small that inter-atomic interactions and quantum mechanical properties need to be studied extensively. Some of these candidates include: hybrid molecular/semiconductor electronics, one-dimensional nanotubes/nanowires, or advanced molecular electronics.
The speed and size of computer chips are limited by how much heat they dissipate. All electronics dissipate heat as a result of the electrons in the current colliding with the device material, a phenomenon called resistive heating. This heating outweighs other smaller thermoelectric effects that can locally cool a device. Computers with silicon chips use fans or flowing water to cool the transistors, a process that consumes much of the energy required to power a device. In silicon and most materials, the electronic heating is much larger than the self-cooling. However, it was found that in these graphene transistors, there are regions where the thermoelectric cooling can be larger than the resistive heating, which allows these devices to cool themselves. This self-cooling has not previously been seen for graphene devices. This self-cooling effect means that graphene-based electronics could require little or no cooling, begetting an even greater energy efficiency and increasing graphene’s attractiveness as a silicon replacement.
With the first observation of thermoelectric effects at graphene contacts, researchers have found that graphene transistors have a nanoscale cooling effect that reduces their temperature. Using an AMF tip to measure temperature, they found that thermoelectric cooling effects can be stronger at graphene contacts than resistive heating, so graphene transistors are self-cooling. The measurements revealed surprising temperature phenomena at the points where the graphene transistor touches the metal connections. They found that thermoelectric cooling effects can be stronger at graphene contacts than resistive heating, actually lowering the temperature of the transistor. Future computer chips made out of graphene — carbon sheets 1 atom thick — could be faster than silicon chips and operate at lower power. However, a thorough understanding of heat generation and distribution in graphene devices has eluded researchers because of the tiny dimensions involved. Graphene electronics are still in their infancy; however, measurements and simulations project that thermoelectric effects will become enhanced as graphene transistor technology and contacts improve.
Latest developments
A team of researchers has discovered a way to cool electrons to minus 228 degrees Celsius without external means and at room temperature, an advancement that could enable electronic devices to function with very little energy. The technology makes use of a chip, which contains nanoscale structures enabling electron cooling at room temperature. The process involves passing electrons through a quantum well to cool them and keep them from heating. This is for the first time to effectively cool electrons at room temperature. Researchers have done electron cooling before, but only when the entire device is immersed into an extremely cold cooling bath. Obtaining cold electrons at room temperature has enormous technical benefits. For example, the requirement of using liquid helium or liquid nitrogen for cooling electrons in various electron systems can be avoided. According to a natural phenomenon, electrons are thermally excited even at room temperature, if that electron excitation could be suppressed, then the temperature of those electrons could be effectively lowered without external cooling. Researchers used a nanoscale structure — which consists of a sequential array of a source electrode, a quantum well, a tunneling barrier, a quantum dot, another tunneling barrier, and a drain electrode — to suppress electron excitation and to make electrons cold.
Cold electrons promise a new type of transistor that can operate at extremely low-energy consumption. Implementing these findings to fabricating energy-efficient transistors is currently under way. This type of research findings represent its role in fostering innovations that benefit the society, such as creating energy-efficient green technologies for current and future generations. With the growing number of electronic devices in day to day use by mankind with a no looking back, research teams have to develop real-world solutions to a critical global challenge of utilizing the energy efficiently and developing energy-efficient electronic technology that will benefit us all every day. When implemented in transistors, these research findings could potentially reduce energy consumption of electronic devices by more than 10 times compared to the present technology. Personal electronic devices such as smart phones, iPads, etc., can last much longer before recharging. In addition to potential commercial applications, there are many military uses for the technology. Batteries weigh a lot, and less power consumption means reducing the battery weight of electronic equipment that soldiers are carrying, which will enhance their combat capability. Other potential military applications include electronics for remote sensors, unmanned aerial vehicles and high-capacity computing in remote operations. Future research could include identifying key elements that will allow electrons to be cooled even further. The most important challenge of this future research is to keep the electron from gaining energy as it travels across device components. This would require research into how energy-gaining pathways could be effectively blocked.
Researchers have also developed a more efficient, less expensive way of cooling electronic devices – particularly devices that generate a lot of heat, such as lasers and power devices. The technique uses a “heat spreader” made of a copper-graphene composite, which is attached to the electronic device using an indium-graphene interface film. Both the copper-graphene and indium-graphene have higher thermal conductivity, allowing the device to cool efficiently. In fact, the copper-graphene film’s thermal conductivity allows it to cool approximately 25 percent faster than pure copper, which is what most devices currently use. The copper-graphene composite is also low-cost and easy to produce. Copper is expensive, so replacing some of the copper with graphene actually lowers the overall cost.
