The electronics industry is always looking for smaller and more efficient devices, especially semiconductors. Because of their prominent applications in the photovoltaic and computer industries— from transistors to solar cells— there has been increasing interest in finding new semiconductor materials and using them to augment current devices.
There are many suitable semiconductor materials, each with subtle variances in their properties that provide advantages and disadvantages in their respective uses. Because industry entrepreneurs are looking to increase the efficiency of semiconductors, there's been increasing interest in developing new semiconducting materials.
Researchers from Stanford University have been experimenting with a material known as molybdenum(IV) telluride (MoTe2), and they believe that it will provide the groundwork for a revolutionarily fast and efficient set of two-dimensional data storage chips.
Now, what makes molybdenum telluride so incredible is that it has a structure with a multitude of electronic applications due to its ability to crystallize uniquely (PDF). Its structure allows it to crystallize into two-dimensional sheets that aren’t just atomically thin, but are flexible and transparent as well.
By nature, MoTe2 is a semiconductor and is also capable of exhibiting photoluminescent properties, a feature frequently sought after in the two-dimensional semiconductor market. However, the simple material does have one more unique property that sets it apart from the rest. MoTe2 has the ability to exist in two different states with electric gate change voltages: an electron-conducting state and a non-conducting state. This specific property allows the storage of information; the two different states can be defined as digital zero or ones, and it just happens to do so using far less material than today’s current technologies.
The research team was challenged to find a way to efficiently elicit a phase change in the MoTe2 chip. Yao Li, a PhD student working with the research team, described how to create an efficient phase change in the material. A diminutive electrical charge is distributed to a specially designed MoTe2 chip which would then switch the crystal from the zero to one state or vice versa. This phase change was revolutionary in the fact that it didn’t rely on pressure or heat to commence the phase change.
A graphical representation of a phase change between non-crystalline to crystalline states. Image courtesy of Phys.org.
Up until now, the common approach to eliciting a phase change in a semiconductor material has been to expeditiously heat up the crystal structure and then immediately cool it down to shift from the zero state to the one state. Unfortunately, various issues arise when rapidly changing temperatures occur in high-density circuits. Not only does this require a large amount of energy to be converted, but it also tends to cause faults in the chip over time.
By comparison, the structural phase transition within the MoTe2 occurs at near room temperature at ultrafast timescales.
The currently prevailing phase-change material used is called germanium-antimony-tellurium or GST. Its crystallization temperature is between 100-150 degrees Celsius and is typically ten-to-one-hundred times thicker than MoTe2. The pure thinness of MoTe2 allows it to make use of electric charges instead of relying on heat to make phase changes. This has implications that could possibly render a shift in phase-change semiconductor materials, as well as broaden the market for new technologies such as smart clothing.
The MoTe2 material has the potential to store data one hundred times faster than our current bulk silicon-based technology used in the majority of memory-based devices such as laptops and smartphones. With the new material premiering in laboratories, researchers intend to design atomically-thin storage devices, possibly ushering a change in our current memory-based technologies.