Showing papers by "Andras Kis published in 2012"

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

Abstract: Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

Breakdown of High-Performance Monolayer MoS2 Transistors

Abstract: Two-dimensional (2D) materials such as monolayer molybdenum disulfide (MoS(2)) are extremely interesting for integration in nanoelectronic devices where they represent the ultimate limit of miniaturization in the vertical direction. Thanks to the presence of a band gap and subnanometer thickness, monolayer MoS(2) can be used for the fabrication of transistors exhibiting extremely high on/off ratios and very low power dissipation. Here, we report on the development of 2D MoS(2) transistors with improved performance due to enhanced electrostatic control. Our devices show currents in the 100 μA/μm range and transconductance exceeding 20 μS/μm as well as current saturation. We also record electrical breakdown of our devices and find that MoS(2) can support very high current densities, exceeding the current-carrying capacity of copper by a factor of 50. Our results push the performance limit of MoS(2) and open the way to their use in low-power and low-cost analog and radio frequency circuits.

Small-signal amplifier based on single-layer MoS2

Abstract: In this letter we demonstrate the operation of an analog small-signal amplifier based on single-layer MoS2, a semiconducting analogue of graphene. Our device consists of two transistors integrated on the same piece of single-layer MoS2. The high intrinsic band gap of 1.8 eV allows MoS2-based amplifiers to operate with a room temperature gain of 4. The amplifier operation is demonstrated for the frequencies of input signal up to 2 kHz preserving the gain higher than 1. Our work shows that MoS2 can effectively amplify signals and that it could be used for advanced analog circuits based on two-dimensional materials.

Long-term retention in organic ferroelectric-graphene memories

Abstract: Long-term stability of high- and low-resistance states in full-organic ferroelectrically gated graphene transistors is an essential prerequisite for memory applications. Here, we demonstrate high retention performance for both memory states with fully saturated time-dependence of the graphene channel resistance. This behavior is in contrast with ferroelectric-polymer-gated silicon field-effect-transistors, where the gap between the two memory states continuously decreases with time. Before reaching saturation, the current decays exponentially as predicted by the retention model based on the charge injection into the interface-adjacent layer. The drain current saturation attests to a high quality of the graphene/ferroelectric interface with low density of charge traps.

Raman and Photoluminescence Study of Dielectric and Thermal Effects on Atomically Thin MoS2

Abstract: Atomically thin two-dimensional molybdenum disulfide (MoS2) sheets have attracted much attention due to their potential for future electronic applications. They not only present the best planar electrostatic control in a device, but also lend themselves readily for dielectric engineering. In this work, we experimentally investigated the dielectric effect on the Raman and photoluminescence (PL) spectra of monolayer MoS2 by comparing samples with and without HfO2 on top by atomic layer deposition (ALD). Based on considerations of the thermal, doping, strain and dielectric screening influences, it is found that the red shift in the Raman spectrum largely stems from modulation doping of MoS2 by the ALD HfO2, and the red shift in the PL spectrum is most likely due to strain imparted on MoS2 by HfO2. Our work also suggests that due to the intricate dependence of band structure of monolayer MoS2 on strain, one must be cautious to interpret its Raman and PL spectroscopy.

1 Nonvolatile Memory Cells Based on 2 MoS 2 /Graphene Heterostructures

Abstract: Memory cells are an important building block of digital electronics. We combine here the unique electronic properties of semiconducting monolayer MoS2 with the high conductivity of graphene to build a 2D heterostructure capable of information storage. MoS2 acts as a channel in an intimate contact with graphene electrodes in a field-effect transistor geometry. Our prototypical all-2D transistor is further integrated with a multilayer graphene charge trappinglayerintoadevicethatcanbeoperatedasanonvolatilememorycell.Becauseofitsbandgapand2Dnature,monolayerMoS2ishighlysensitiveto the presence of charges in the charge trapping layer, resulting in a factor of 10 4 difference between memory program and erase states. The two

MoS2-based devices and circuits

Abstract: Two-dimensional crystals offer several inherent advantages over conventional 3D electronic materials or 1D nanomaterials such as nanotubes and nanowires. Their planar geometry makes it easier to fabricate circuits and complex structures by tailoring 2D layers into desired shapes. Because of their atomic scale thickness, 2D materials also represent the ultimate limit of miniaturization in the vertical dimension and allow the fabrication of shorter transistors due to enhanced electrostatic control. Another advantage of 2D semiconductors is that their electronic properties (band gap, mobility, work function) can be tuned for example by changing the number of layers or applying external electric fields.

Micro-fabrication process for small transport devices of layered manganite

Abstract: Devices have been fabricated based on the bilayer manganite La1.4Sr1.6Mn2O7, which in the bulk state orders magnetically below 90 K, at which point both in-plane and c-axis bulk resistivity decrease by 2-3 orders of magnitude. We provide an optimized procedure to fabricate devices to electrical transport in- and out of plane. Fabricated mesoscopic devices have dimensions comparable to a typical magnetic domain, allowing us to study structures going from a single domain to several domains.