NIST and UMD Work to Develop a Transistor Device as Thick as a Single Atom

A New Wave of Transistors

Moore's Law is a familiar rule that refers to Gordon E. Moore’s perception that the number of transistors on a microchip doubles every two years. In order to stay on track with Moore’s Law, researchers must find a way to make many copies of atomic-scale transistor devices.

Artist’s illustration of a part of the method developed at NIST to make single-atom transistors. Image used courtesy of NIST.

 

 

Scientists at NIST and UMD became the second group to construct a single-atom transistor. This month, the researchers demonstrated how to precisely adjust the rate at which individual electrons flow through a physical gap in a transistor.

Ignoring the laws of physics which forbid electrons from any movement due to the lack of energy, this groundbreaking process will alter the future of microchip development by yielding single-atom transistors.

NIST and UMD are sharing their innovative recipe for these miniature transistors with the rest of the world.

 

Microchips could be equipped with atom-thick transistors to improve processors. Image courtesy of Pixabay.

 

Components

• Silicon Wafer
• Hydrogen Atoms
• Phosphine Gas
• Palladium Metal

 

How They did it

• Begin by taking a silicon wafer made of layered silicon atoms and deposit hydrogen atoms on top.
• Using a Scanning Tunneling Microscope (STM), remove hydrogen atoms to create a mask that will define the geometry of the transistor.
• Direct phosphine gas at the surface, this will stick to where the hydrogen atoms have been removed.
• The phosphorous molecules will break apart and the phosphorous atoms substitute one layer down into the silicon lattice.
• At room temperature, add a silicon layer on top and remove hydrogen atoms. This step will separate you from all other developers.
• Now bake the lattice to remove any defects to ensure a uniform crystal structure remains.
• Add a second layer of uniformed silicon crystal on top to create contacts.
• Apply palladium metal to the surface in specific locations. The palladium is then heated, diffusing into the silicon and creating regions of palladium silicide. 
• Newly formed regions allow for making electrical contacts with the buried phosphorous atoms.  
• After the lattice cools, the process of fabricating single-atom transistors is complete.

 

Before this group of researchers came along, developers typically had to apply heat as all the silicon layers are grown in order to remove defects. However, NIST and UMD scientists found that such heating could dislodge the bound phosphorus atoms and potentially disrupt the structure of the device, according to a news release from NIST. Instead, the team deposited the first several silicon layers at room temperature, allowing the phosphorus atoms to hold.

 

Transistors in Power Electronics

Sometimes taken for granted, unseen transistors are utilized in relays, DC motors, transformers, inverters, converters, and power demands that require solid-state switching. They can be used to regulate current or amplify an input signal into the greater output signal. 

 

Isolated, unregulated 1-2W DC/DC converters suitable for the Industrial, Transportation, Telecom, and Datacom markets. Image used courtesy of Flex Power Modules.

 

Isolated, unregulated 1-2W DC/DC converters suitable for the Industrial, Transportation, Telecom, and Datacom markets. Image used courtesy of Flex Power Modules.

Various types of transistors are used in power electronics, one, in particular, is the insulated gate bipolar transistor (IGBT) which is a cross between bipolar junction transistor (BJT) and a metal oxide semiconductor field-effect transistor (MOSFET). This combination yields a device with high impedance and high switching speeds. IGBTs provide lower on-resistance and conduction losses as well as its ability to switch high voltages at high frequencies without damage. An ideal characteristic for driving inductive loads and converters similar to the PUB-M from Flex Power Modules.

 

Downsizing to Increase Capabilities 

We know the more transistors we can add to a single chip the better right? But what kind of impact does that actually make? As engineers pack more and more circuitry on a tiny computer chip the gap between components continues to shrink.

The research team with NIST and UMD discovered that by increasing or decreasing the gap between transistor components by less than a nanometer, they could precisely control the flow of a single electron through the transistor. Establishing the ability to control the flow of one electron at a time is a significant achievement.

Once unimaginable, transistors consisting only of single atoms promise to become the building blocks of a new generation of computers with unparalleled memory and processing power.