Saptarshi Das

Research

Low dimensional materials are extremely interesting as they not only offer fundamental study of novel physical phenomenon, but also their unique electrical, optical, mechanical and chemical properties make them attractive from a technological standpoint.Nanotubes, Nanowires, Graphene, hexagonal boron nitride (h-BN) and more recently the rich family of transition metal di-chalcogenides – comprising of MoS2, WS2, WSe2 and many more - have received a lot of scientific attention as the future of nanoelectronics My research covers a broad range of experimental effort on these novel low dimensional materials based field effect transistors for high performance and low power logic and memory applications.

 

Layered 2-D Semiconducting Di-chalcogenides (MoS2, WSe2, WS2)

The transition metal di-chalcogenide family (MX2, with M being any transition metal and X= S, Se, Te) offers a wide range of materials with unique properties. They can be metallic, semiconducting as well as insulating. Many of these materials are available in 2-D layered crystal form. The individual layers are held together by weak van der Waals interlayer interaction, and, therefore, allows for micromechanical exfoliation of mono or few layers – similar to the fabrication of graphene from graphite. The ultra-thin semiconducting di-chalcogenides can potentially become the backbone of future nanoelectronics. My research explores the ultimate potential of ultra thin MoS2 based field effect transistors for low power and high performance logic applications.

Integration of Silicon Nanowire Transistor with Ferroelectric Materials

Silicon has continued to be the corner stone of the entire semiconductor industry for several decades. Silicon nanowires, are therefore, extremely attractive candidate for low power, high performance future nanoelectronics from a technological standpoint. However in order to boost the performance of silicon based devices, there is an increasing trend toward integration of silicon with other materials.My research explores next generation logic and memory devices based on the integration of Silicon nanowire with ferroelectric materials.

Tunneling Field Effect Transistors

After decades of research, development and technological implementation, the silicon evolutionary path is nearing an end. The non scalability of the subthreshold swing (SS) to below 60mV/decade (at room temperature) has resulted in a significant increase in the OFF-state current making the standby power dissipation comparable with the active switching power. In order continue the scaling and thereby improving the overall device performances alternative concepts are being proposed. The Tunneling Field Fffect Transistor (TFET) based on the concept of energy filtering is one of those promising solutions.

 

Graphene Field Effect Transistors for RF applications

My theoretical research on Graphene is motivated to identified the ideal bandgap value in graphene devices, e.g. through size quantization in graphene nano-ribbons, to enable graphene based high performance RF applications. When considering a ballistic graphene nano-ribbon low noise amplifier (GNR-LNA), including aspects like stability, gain, power dissipation and load impedance, our calculations predict a finite bandgap of the order of Eg≈100meV to be ideally suited. GNR-LNAs with this bandgap, biased at the optimum operating point are ultra-fast (THz) low noise amplifiers exhibiting performance specs that show considerable advantages over state-of-the-art technologies. The optimum operating point and bandgap range is found by simulating the impact of the bandgap on several device and circuit relevant parameters including transconductance, output resistance, band-width, gain, noise figure and temperature fluctuations.

 

             

Saptarshi Das