Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session U39: Focus Session: Emerging Research Devices and Materials for the Microelectronics Industry II |
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Sponsoring Units: FIAP Chair: Victoria Soghomonian, Virginia Polytechnic Institute and State University Room: Colorado Convention Center 502 |
Thursday, March 8, 2007 8:00AM - 8:12AM |
U39.00001: Transfer printed organic thin-film transistors using the semiconductors P3HT or pentacene and a polymer dielectric. Adrian Southard, Dan Hines, Elba Gomar-Nadal, Ellen Williams, Michael Fuhrer The assembly via the transfer printing process of all components for organic electronic devices onto a plastic substrate has been demonstrated. Both poly(3-hexylthiophene) (P3HT) and pentacene (Pn) have been used as active semiconducting films for such devices without exposing the films to detrimental chemical processes. Transfer printing relies on the difference in adhesion of two substrates towards the material being transferred. Here we use the transfer printing process to fabricate organic thin-film transistors (OTFT) with a range of channel lengths. These devices are used to characterize the contact resistance for both the P3HT and Pn OTFTs. The field-effect mobility of the P3HT devices is measured to be in the range of 0.02 to 0.035 cm$^{2}$/(Vs) which is comparable to the best values reported in the literature and is an order of magnitude higher than the control devices of the unprinted P3HT film as deposited onto a SiO$_{2}$ dielectric layer. These devices are demonstrated using polystyrene (PS), poly(4-vinylphenol) (PVP) and poly methylmethacrylate (PMMA) as dielectric materials and polyethylene terephthalate (PET) as the substrate material. [Preview Abstract] |
Thursday, March 8, 2007 8:12AM - 8:24AM |
U39.00002: First-principles calculations of mobilities in MOSFETs George Hadjisavvas, Leonidas Tsetseris, Matthew Evans, Sokrates Pantelides Nano-scale MOSFETs demonstrate interesting electron transport behavior. Straining the silicon lattice results in significant increases in carrier mobility up to 100{\%}. Transport properties are known to depend also on the presence of interface traps. Due to their significance, a large number of studies have obtained mobilities, but in an empirical and semi-classical fashion, whereas, in nano-devices quantum mechanical effects and atomic-scale structural details are the key factors of mobility calculations. Here we use a recently developed method[1] for first-principles calculations of mobilites within DFT to probe the effect of strain and interface point defects (e.g., dangling bonds) on mobilities in double gate ultra-thin SOI (UTSOI) MOSFETs. The transport properties are described in a fully self-consistent quantum mechanical fashion and mobilities are calculated within the Born approximation. The results show that biaxial tensile strain is shown to significantly increase carrier mobility in UTSOI devices by suppressing the effective scattering from atomic-scale interface inhomogeneities; the effect of dangling bonds on mobility in a UTSOI channel is weaker than in conventional MOSFETs because the carrier density peaks at the center of the channel. This work was supported in part by NSF Grant ECS-0524655 and by AFOSR Grant 4224224232. [1] M.H. Evans et al., Phys. Rev. Lett. \textbf{95, }106802 (2005). [Preview Abstract] |
Thursday, March 8, 2007 8:24AM - 8:36AM |
U39.00003: Nano-circuit design in the nonohmic regime Vijay Arora Ohm's law on the basis of which all electronic circuits are designed and their performance evaluated is not holding its linearity as nanoelectronic devices are scaled down. In a macro-device of twentieth century (typical size L = 1 cm), the critical voltage for triggering nonohmic behavior, $V_c =\frac{V_t }{\ell _o }L$, is 2.6 kV for the room-temperature thermal voltage $V_t =\frac{k_B T}{q}$ = 26 mV and a typical ohmic mean free path = 0.1 $\mu $m. For the integrated circuits, a 5-V logic voltage was within the ohmic regime. For the twenty-first century nano-circuits, a typical device size, L, is below 0.1 $\mu $m, resulting in a critical voltage of 0.26 V. Even for a low logic voltage of 1 V, Ohm's law is not valid. A review of the physical processes behind this breakdown of Ohm's law is reviewed. The paper will show how familiar voltage and current division laws and the transient effects transform in the nano-regime where Ohm's law is not valid. In a circuit environment, the smaller-length resistor is much more resistive as applied voltage is increased. Similarly, RC time constant will be larger than its expected ohmic value. Power consumption in the nano-circuit tends to be linear function of the applied voltage in direct contrast to quadratic dependence for the macro circuits. [Preview Abstract] |
Thursday, March 8, 2007 8:36AM - 8:48AM |
U39.00004: Emission from Vertical-Cavity Surface-Emitting Lasers after Femtosecond Pulse Injection Botao Zhang, Albert Heberle Vertical-cavity surface-emitting lasers (VCSEL's) are important devices for optical communication and sensing. Many applications require single-mode operation, which can be achieved by suppressing multiple lateral modes with emission apertures of 10 micrometers or less and by restricting emission to one polarization by reduction of symmetry. Such single-mode lasers still can produce multi-mode emission when subject to high pump currents or high-frequency modulation. Here we will discuss the emission dynamics of single-mode VCSEL's after resonant optical injection of femtosecond pulses from a mode-locked Ti:sapphire laser. The VCSEL emission is time and polarization resolved by cross correlation on a nonlinear optical crystal. This all-optical technique gives access to the VCSEL dynamics without limitation from electronics. Our measurements show dynamics in the 10 GHz range stemming from ordinary and from polarization relaxation oscillations. Interference beats above 100 GHz show the importance of dynamic multi-mode behavior. The decay of these beats gives direct information on the roundtrip gain of the dynamically excited modes. Polarization resolved measurements show the feasibility of polarization switching on a subpicosecond time scale. [Preview Abstract] |
Thursday, March 8, 2007 8:48AM - 9:00AM |
U39.00005: Photon storage with ultrafast switching in coupled quantum wells Alexander Winbow, Aaron Hammack, Leonid Butov, Arthur Gossard Photon storage with ultrafast switching was implemented with indirect excitons in coupled quantum wells. The storage and release of photons was controlled by the gate voltage: a pulse of the gate voltage increased the exciton lifetime by orders of magnitude, resulting in storage of the absorbed photons in the form of indirect excitons; the pulse termination led to the emission of the stored photons. The storage time reached microseconds. The write and readout times were subnanosecond, and faster by an order of magnitude than the previously established record for optoelectronic photon storage devices. [Preview Abstract] |
Thursday, March 8, 2007 9:00AM - 9:12AM |
U39.00006: High-Power, Single-Mode, Distributed-Feedback Interband Cascade Lasers for the Midwave-Infrared M. Kim, C.S. Kim, W.W. Bewley, C.L. Canedy, J.A. Nolde, J.R. Lindle, I. Vurgaftman, J.R. Meyer Narrow-ridge distributed-feedback interband cascade lasers with HR/AR coating have been fabricated using e-beam lithography followed by Ge lift-off. The quarter wavelength phase shift region has also been introduced near the HR coating facet to robust single mode operation with better wavelength control. Furthermore, amorphous Si layers have been deposited both sides of ridges to keep the single mode for wider ridge width ($\sim $13 $\mu $m) by suppress the additional transverse modes. A single-mode output has been obtained at $T$ = 130 K and $\lambda \approx $ 3.313 $\mu$m. [Preview Abstract] |
Thursday, March 8, 2007 9:12AM - 9:48AM |
U39.00007: The Role of Physics in New Information Processing Technologies Invited Speaker: As semiconductor technology moves ever closer to the ultimate physical limits for scaling of devices that utilize electrons as information bearing particles, many new opportunities for research in the physical sciences are emerging. In order to achieve the limits for electron transport scaling, many new materials and processing problems must be overcome including the invention of both low and high dielectric-constant material technologies and new ideas for interdevice communication. If we look beyond the limits of scaling electron devices, many more challenging research opportunities exist in the areas of physics of information carriers and physics of communication. On the physics of information carriers, it may be that for devices with critical dimensions less than one nanometer, an information bearing particle much more massive than the electron would be desirable. As another example, we have observed that for spin-based systems, high magnetic fields are needed for reliable spin manipulation. Breakthroughs in the physics of spin manipulation are needed. For example is it possible to obtain suitable materials that exhibit a high g-factor to enable controllable devices that operate with reasonable energies and magnetic fields. The option operation in a non-equilibrium thermal environment also needs to be considered. On the physics of communication, for branched communication between nanodevices, it may be that we need to supplant metallic or nanotube interconnects with systems that utilize the wave nature of quantum particles to minimize energy dissipation. [Preview Abstract] |
Thursday, March 8, 2007 9:48AM - 10:00AM |
U39.00008: Modeling of resonant terahertz detector with two-dimensional electron gas and lateral Schottky junction Nizami Vagidov, Akira Satou, Victor Ryzhii, Michael Shur, Vladimir Mitin We developed a device model for a resonant detector of terahertz (THz) radiation based on a heterostructure with an ungated two-dimensional electron channel and with a lateral Schottky junction at one of the channel edges (recently proposed and assessed by us using an analytical model). The resonant operation of the detector is associated with the excitation of electron plasma oscillations in the channel with the channel serving as a resonant cavity for the plasma waves. The rectification of the signals is due to nonlinearity of the lateral Schottky junction current-voltage characteristics. The model comprises a kinetic equation governing the electron transport in the device channel and a two-dimensional Poisson equation for the self-consistent electric potential. A novel approach, accounts for the electron-electron collisions and other scattering mechanisms, is used for numerical solution of the equations of the model. Using the developed model, we studied the resonant excitation of plasma oscillations by incoming terahertz signals and calculated the detector responsivity at different levels of excitation of the plasma oscillations. The THz detector performance is compared with that of Schottky diodes without the plasma resonant cavity. [Preview Abstract] |
Thursday, March 8, 2007 10:00AM - 10:12AM |
U39.00009: Si single electron tunneling transistor with tunable barriers Emmanouel Hourdakis, Neil Zimmerman, Stuart Martin, Akira Fujiwara, Hiroshi Inokawa, Kenji Yamazaki, Hideo Namatsu, Yashuo Takahashi, Yukinori Ono We demonstrate the operation of single-electron tunneling (SET) transistor using electrostatically induced barriers. The barriers are formed on a Silicon nanowire using metal-oxide-metal field effect transistor (MOSFET) gates. This allows us to control the conductance of the tunnel barriers by more than 3 orders of magnitude. It also allows for various configurations of charge islands (changing the gate used for the tunnel barrier changes the shape and size of the island ). Below 4 K, the Coulomb blockade oscillations obtained are highly periodic. We also report the excellent reproducibility of the value of gate capacitances between different devices (variation of about 1 aF). The excellent controllability in these devices increases their potential in a number of applications, like metrological current standard or multivalued memory. [Preview Abstract] |
Thursday, March 8, 2007 10:12AM - 10:24AM |
U39.00010: Extraordinary Electroconductance in In-GaAs hybrid thin film structures Yun Wang, A.K.M. Newaz, K.A. Wieland, S.A. Solin Following the demonstration of extraordinary electroconductance (EEC) in metal-semiconductor hybrids (MSHs) in macroscopic structures, we have developed a new design for a microscopic thin film EEC sensor, which is a van der Pauw plate structure consisting of a heavily doped n-type GaAs epi layer (500nm) with metallic shunt (50nm) on top. EEC arises from the current redistribution between the shunt and GaAs when an external E field lowers the interfacial Schottky barrier height (SBH). By defining the EEC effect to be the percentage change in sample conductance with and without the E field, we have obtained a 20\% change in the macroscopic sample in a field of 12kV/cm at 300K. We also compared the response of a sample with a Schottky barrier to an unshunted sample and to a shunted sample with an Ohmic interface. We propose that by applying a new surface treatment to the GaAs mesa, the surface state density can be remarkably reduced, so that the SBH is controlled by judicious choice of the metal. This allows more electron transport over the barrier and results in a geometrically enhanced conductance change. By varying the geometry of the structure and the material of the shunt, we can optimize the design of the EEC sensor. [Preview Abstract] |
Thursday, March 8, 2007 10:24AM - 10:36AM |
U39.00011: Investigating the resonant response of a field-effect transistor subjected to an ac signal Manvir Kushwaha A theoretical investigation is made of the response of a field-effect transistor (FET) to an incoming electromagnetic radiation in the presence of a perpendicular magnetic field within the framework of hydrodynamics. The treatment is valid for a nondegenerate electron gas in which the mean free path for electron-electron scattering $\lambda_{ee}$ is much smaller than the device length $L$ and than the mean free path due to collisions with impurities and/or phonons $\lambda_{coll}$. These requirements, written as $\lambda_{ee} \ll L \ll \lambda_{coll}$, are fulfilled for magnetic fields weak enough to prevent Landau quantization. It is our general observation that the shorter device lengths, weaker magnetic fields, and lower temperatures (or higher electron mobility) are most favorable to achieve a greater resonant response of the device to an ac signal. Such resonant response makes FET a promising device for new types of sources, detectors, mixers, and multipliers in the GHz and THz frequency range. [Preview Abstract] |
Thursday, March 8, 2007 10:36AM - 10:48AM |
U39.00012: Resistance Switching Behavior in Epitaxial NiO Films Seung Ran Lee, Jino Lee, Kookrin Char Recently NiO has attracted great attention due to its potential applications for nonvolatile ReRAM devices. However, the mechanism of resistance switching has not been clearly elucidated and it still remains controversial. To understand the phenomena in resistance switching, epitaxial film can serve as a good model system. Epitaixial films show atomically flat surface as well as good crystallization with much fewer defects which have been considered to be responsible for resistance switching behavior in polycrystalline NiO (poly-NiO). For these purposes we have grown epitaxial NiO (epi-NiO) films on SRO films prepared on (100) STO by pulsed laser deposition systems. XRD pattern shows clear (200) NiO peaks, which means our films are well crystallized with minimal defects. We also analyzed AFM and TEM images of SRO/NiO/Pt, which show clean and atomically flat interface between each layer. I-V characteristics of epi-NiO show an asymmetric shape and bipolar switching behavior. No abrupt current increase at ambient voltage was found, which is considered to be a necessary process for resistance switching in poly-NiO. These results suggest that unidentified defect states and/or interfaces play an important role in resistance switching phenomena. In order to understand the role of defects and interfaces further, our efforts to control the density of defect states and correlate them with I-V characteristics will be presented. [Preview Abstract] |
Thursday, March 8, 2007 10:48AM - 11:00AM |
U39.00013: Nanowire Non-volatile Memory with Silicon Nitride Charge Trapping Layer Qiliang Li, Xiaoxiao Zhu, D.E. Ioannou, J.S. Suehle, C.A. Richter We present the fabrication and characterization of Si nanowire field effect transistors with silicon nitride as a charge trapping layer for non-volatile memory application. The Si nanowires were grown by chemical vapor deposition on defined location on a 60 nm Si nitride which was deposited on a 20 nm thermal grown oxide (blocking oxide). The source/drain electrodes were formed by using photolithographic alignment and metal lift-off processes. The nanowires were then covered with sputtering oxide at room temperature to be isolated from the external environment. We have observed a large threshold voltage shift window (8 V) at 10 V write/erase voltage and non-volatile on/off current states, which is attributed to the small radius ($\sim $ 10 nm) and intrinsic doping of the Si nanowire. The dynamics of the nanowire/nitride charge exchange, and its effect on threshold voltage and memory retention have been studied. [Preview Abstract] |
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