a team of researchers at the national institute for materials sciences (tsukuba, japan) have created a new fabrication process for building diamond-based transistors that could replace silicon technology in high-powered electronics or in harsh environments like engines or cosmic ray bombardment in space.

researchers are exploring news methods for creating diamond transistors.
(wikimedia commons)

the process was described in an article from the american institute of physics (aip).

researchers have turned to diamonds in the past because they are physically hard, while also being good conductors of heat and capable of enduring larger voltages than current semiconductor materials.

“the research group focused their work on enhancement-mode metal-oxide-semiconductor field-effect transistors (mosfets), a type of transistor that is commonly used in electronics,” the article explained. “one of the distinguishing features of transistors is inclusion of an insulated terminal called a ‘gate’ whose input voltage determines whether the transistor will conduct electricity or not.”

according to one of the researchers, the team deposited yttrium oxide (y­₂o₃) insulator directly on the surface of the diamond to form the gate. they used electron beam evaporation to perform this process. this entails using a beam of electrons to turn y­₂o₃ from solid to gas to cover the surface and then solidify on it.

building on previous work, the researchers deposited the y­₂o₃ as a single layer, which makes it easier and cheaper to manufacture.

the article added, “yttrium oxide 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.”

the work was recently published in applied physics letters. the abstract stated:

“enhancement-mode (e-mode) hydrogenated diamond (h-diamond) metal-oxide-semiconductor field-effect transistors (mosfets) are fabricated with an y₂o₃ oxide insulator grown on the h-diamond directly using an electron beam evaporator.

“the depletion region of the capacitance-voltage curve for the mos capacitor shifts to the left hand side relative to 0 v, which indicates the existence of positive charges in the y₂o₃ film. there are distinct pinch-off and p-type channel characteristics of the y₂o₃/h-diamond mosfets. the maximum drain-source current for the mosfet without interspace between the source/drain and the gate (l_s/d-g) is −114.6 ma mm⁻¹.

“those for the mosfets with l_s/d-g are decreased from −11.0 to −2.1 ma mm⁻¹ with the gate length increasing from 3.3 ± 0.1 to 15.4 ± 0.1 μm. threshold voltages for all the mosfets are negative, indicating their e-mode characteristics. 

“negatively charged adsorbates are one of the necessary conditions for hole accumulation of the h-diamond channel layer, which are possibly compensated by the positive charges in the y₂o₃ film, resulting in e-mode characteristics of the mosfets.”