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ABSTRACT: In this study, we have developed conductive tips with high aspect ratio and good sharpness by scanning electron beam induced deposition (SEBID) method. The structure and morphology of modified conductive tips were performed by analytical transmission electron microscopy (TEM) methods. Atomic force microscope (AFM), scanning Kelvin probe microscopy (SKPM) and electrostatic force microscopy (EFM) analysis were done by using these modified tips and compared to standard commercially scanning probe microscopy (SPM) probes. The SEBID modified tips demonstrate signals with smaller full-width at half-maximum (FWHM) value in EFM measurements. The prepared tips could provide high spatial resolution and high stability to avoid a perturbation of the sensor characterization due to the sample's stray field.
01/2012;
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ABSTRACT: In this paper, we present our study of the maximum electron density, nmax, accessible via low-temperature transport experiments in enhancement-mode Si/Si1−xGex heterostructure field-effect transistors. Experimentally, we find that nmax is much higher than the value obtained from self-consistent Schrödinger-Poisson simulations and that nmax can be changed only by changing the Ge concentration in the Si1−xGex barrier layer, not by varying the barrier layer thickness. The discrepancy between experiments and simulations is explained by a non-thermal-equilibrium tunneling-limited model.
Applied Physics Letters 10/2011; 99(15):153510-153510-3. · 3.84 Impact Factor
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ABSTRACT: Well-behaved Ge n-channel metal-oxide-semiconductor field-effect transistors on (001) substrates with dispersion-free, high on/off ratio, and high peak mobility are demonstrated. The interface trap density is effectively reduced down to 5 × 1011 cm−2 eV−1 near midgap by GeO2 passivation using rapid thermal oxidation, resulting in high peak mobility of ∼1050 cm2/Vs. The fast roll-off of the mobility at high electric field is probably due to the large surface roughness scattering. By applying uniaxial 〈110〉 tensile strain (0.08%) on 〈110〉 channel direction, the best mobility enhancement (12%) can be achieved. The calculated strain responses with proper stress configurations are consistent with experimental results.
Applied Physics Letters 07/2011; 99(2):022106-022106-3. · 3.84 Impact Factor
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ABSTRACT: The effects of in situ
prepulse treatment on the bottom Pt electrode of a metal–insulator–metal (MIM) capacitor prior to
atomic layer deposition process were investigated for the first time. The cross-sectional transmission electron microscopy
(TEM) shows a thicker
layer on the
prepulsed Pt surface than that on the no-prepulsed Pt surface. According to TEM results and grazing incidence X-ray diffraction,
it shows that the polycrystallization of the
film with the predominant monoclinic phase can be suppressed when the bottom Pt electrode was pretreated by
pulses. X-ray photoelectron spectroscopy indicated that the surface of the bottom Pt electrode was hydroxylated, which was
considered to be able to facilitate metallorganic precursor bonding with –OH groups on the Pt surface. Atomic force microscopy
reveals that the roughness on the
film surface decreases with increasing
prepulse cycles. Symmetrical leakage current density versus applied voltage
curves were observed. Lower capacitance densities and reduced
of the
-prepulsed samples can be attributed to a thicker dielectric layer. A
MIM capacitor has a capacitance density of
, the quadratic voltage coefficient of capacitance
of
, and
of
at
and at room temperature.
Journal of The Electrochemical Society. 01/2011; 158(2):H128-H131.
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ABSTRACT: A capacitorless single-transistor (1T) memory cell with a long data-retention time is demonstrated on polycrystalline silicon thin-film transistors (TFTs). A new operation mode using channel traps is employed to modulate the drain current in the accumulation region. The different drain current can be read by modulating the barrier height at the grain boundary. The extrapolated retention time at the half of the current window is ~10<sup>7</sup> s. There is no degradation after 2000 write/erase cycles by trap-assisted tunneling programming. The low-temperature process of the TFT cells is attractive for the 3-D integration.
IEEE Electron Device Letters 11/2010; · 2.85 Impact Factor
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ABSTRACT: Recent advances in Wireless Sensor Networks (WSNs) make them more important to apply. Therefore, security issues are more significant in WSNs. WSNs are susceptible to some types of attacks since they are consisted of cheap and small devices and are deployed in open and unprotected environments. In this research, an Intrusion Detection System (IDS) created in cluster head is proposed. The proposed IDS is a Hybrid Intrusion Detection System (HIDS). It consists of anomaly and misuse detection module. The goal is to raise the detection rate and lower the false positive rate by the advantages of misuse detection and anomaly detection. However, a decision-making module is used to integrate the detect results and to report the types of attacks.
Computer Science and Information Technology (ICCSIT), 2010 3rd IEEE International Conference on; 08/2010
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ABSTRACT: We have realized complementary devices on an undoped Si/SiGe substrate where both two-dimensional electrons and holes can be induced capacitively. The design of the heterostructure and the fabrication process are reported. Magnetotransport measurements show that the induced two-dimensional electron gas exhibits the quantum Hall effect characteristics. A p-channel field-effect transistor is characterized and the operation of an inverter is demonstrated. The proof-of-principle experiment shows the feasibility of integrating complementary logic circuits with quantum devices.
Applied Physics Letters 06/2010; 96(25):253103-253103-3. · 3.84 Impact Factor
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ABSTRACT: Strong enhancement of Ge direct transition by biaxial-tensile strain was observed. The reduction in band gap difference between the direct and indirect valleys by biaxial tensile strain increases the electron population in the direct valley, and enhances the direct transition. The band gap reduction in the direct and indirect valleys can be extracted from the photoluminescence spectra and is consistent with the calculations using k⋅p and deformation potential methods for conduction bands and valence bands, respectively.
Applied Physics Letters 05/2010; 96(21):211108-211108-3. · 3.84 Impact Factor
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ABSTRACT: The hexagonal shapes of Si <sub>0.13</sub> Ge <sub>0.87</sub> quantum dots (QDs) and rings on Si(110) reflect the lattice symmetry of the top two Si layers on Si, which is different from that on Si(100). The formation time of nanorings on Si(110) is much longer than that on Si(100). This is probably due to the slow diffusion of Ge and Si on Si(110) substrate. Based on both transmission electron microscopy and Raman spectroscopy, the formation of SiGe nanorings can be attributed to Ge outdiffusion from the top of the central SiGe QDs during in situ annealing. Moreover, the Si cap layer is essential for nanorings formation. The uncapped QDs cannot transform into rings even after a long time annealing.
Journal of Applied Physics 04/2010; · 2.17 Impact Factor
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ABSTRACT: Both direct and indirect transitions of photoluminescence and electroluminescence are observed in a Ge n+p diode. The relative intensity of direct radiative recombination with respect to indirect radiative recombination increases with the increase in the optical pumping power, injection current density, and temperature. The increase in electron population in the direct valley is responsible for the enhancement. The spectra can be fitted by the combination of direct and indirect transition models. The direct radiative transition rate is ∼ 1600 times of the indirect transition, estimated by electroluminescence and photoluminescence spectra near room temperature.
Applied Physics Letters 03/2010; 96(9):091105-091105-3. · 3.84 Impact Factor
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ABSTRACT: This paper proposes a design of IT memory cells that utilizes the modulation of drain current by channel traps and offers these advantages: 1. capacitorless structure, 2. long data retention time, 3. excellent endurance characteristics, 4. low power consumption, 5. 3D integration compatibility.
Semiconductor Device Research Symposium, 2009. ISDRS '09. International; 01/2010
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ABSTRACT: A simple Ge-on-glass metal-oxide-semiconductor solar cell has been demonstrated by wafer bonding and smart-cut. Since single crystalline Ge is directly bonded on glass, the crystalline substrate is not necessary. The metal-oxide-semiconductor structure can be easily fabricated without n and p dopant diffusion or implantation. The reason for low efficiency is discussed, and then the optimized structures are designed by simulation. An outstanding enhancement on efficiency can be achieved with the Si/Ge/Si structure. The best performance can be achieved by optimization of the position of the Ge layer, the thickness of the Ge layer, and the number of the Ge layers. The efficiency of the thin film Si/Ge/Si solar cell with single layer of 30-nm-thick Ge outside the depletion region reaches 15.9%, as compared to the control Si sample of 11.8%. Based on the simulation and technologies, high efficiency thin film solar cells can be demonstrated in the future.
Journal of Nanoscience and Nanotechnology 07/2009; 9(6):3622-6. · 1.56 Impact Factor
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ABSTRACT: The band edge emission with the peak at 1.15 μ m is observed at room temperature from monocrystalline silicon solar cell at forward bias. The electroluminescence spectra can be fitted by electron hole plasma recombination model. The temporal response of electroluminescence is used to characterize the minority carrier lifetime by fitting the time evolution of radiative recombination using the Shockley–Read–Hall, radiative, and Auger recombination models. The minority carrier lifetime is almost constant (1.8 ms) for excess carrier density lower than 4×10<sup>15</sup> cm <sup>-3</sup> , and then decreases at higher concentration.
Journal of Applied Physics 06/2009; · 2.17 Impact Factor
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ABSTRACT: This paper presents an improved SPICE macromodel of phase change random access memory (PCRAM). Based on the circuit-based model architecture in [1], the novelty of this work lies in (1) accurate modeling the current-voltage (I-V) plot including the snapback phenomenon, and (2) solution to the falling edge problem to avoid misrepresentation of the PCRAM state, and (3) calibration of the crystallization time for potential multilevel (ML) operation of the PCRAM.
VLSI Design, Automation and Test, 2009. VLSI-DAT '09. International Symposium on; 05/2009
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ABSTRACT: We report the observation of a two-dimensional electron gas (2DEG) in a Si quantum well with mobility 1.6×106 cm2/V s at carrier densities n ≥ 1.5×1011/cm2. The 2DEG, which resides in an undoped Si/SiGe heterostructure, is capacitively induced using an insulated-gate field-effect transistor (IGFET) device structure; its mobility is determined from transport and quantum Hall effect measurements at 0.3 K. Our IGFET device makes it now possible to access by transport experiments the low electron density regime down to n ∼ 1×1010/cm2.
Applied Physics Letters 05/2009; 94(18):182102-182102-3. · 3.84 Impact Factor
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ABSTRACT: Raman shifts are investigated on silicon and germanium substrates under the uniaxial tensile strain on various substrate orientations. The strain splits the triply degenerate optical (LO, TO) phonons at the zone center (k⃗≈0) . The redshifts of Si Raman peaks induced by the tensile strain on all substrate orientations are observed. With the specific polarization of the incident light, however, the unusual blueshifts of Ge Raman peaks induced by the tensile strain are observed on (110) and (111) Ge substrates. By using the suitable phenomenological constants and taking the Raman selection rules into consideration, the experimental results are in reasonable agreement with the lattice dynamical theory.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
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ABSTRACT: Si-based photodetectors for narrow-band ultraviolet light (319 nm) and green light (500 nm) detection are demonstrated using a metal-oxide-semiconductor tunneling structure. By using appropriate selection of gate metal, the metal-oxide-semiconductor tunneling diode can detect specific range of light. Due to the spectral dependence of absorption and reflection of the Ag and Au as gate electrodes, the narrow-band detection of ultraviolet and green light can be achieved, respectively. The photodetectors with 130 nm thick Ag gate and 70 nm thick Au gate exhibit peak responsivities of 5.1 and 0.3 mA/W at 319 and 500 nm, respectively.
Applied Physics Letters 02/2009; 94(6):061114-061114-3. · 3.84 Impact Factor
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ABSTRACT: In this paper, we have numerically investigated the electrical characteristics of a saddle-like FinFET for sub-50nm DRAMs with a 3D device simulator.
01/2009;
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ABSTRACT: The negative and positive bias temperature instabilities are investigated on p-channel and n-channel TFTs with four different combinations. The stress-induced hump in the subthreshold region is observed for PBTI on p-channel TFTs and NBTI on n-channel TFTs. The hump is attributed to the edge transistors along the channel width direction. Higher electric field at the corners induces more trapped carriers in the insulator as compared to channel transistor. In contrast, no humps are observed for NBTI on p-channel TFTs and PBTI on n-channel TFTs. For NBTI on p-channel TFTs, the interface traps are generated by breaking the Si-H bonds and are responsible for the negative ¿V<sub>T</sub>. On the other hand, electrons are trapped in the insulator and induce positive ¿V<sub>T</sub> for PBTI on n-channel TFTs.
Solid-State and Integrated-Circuit Technology, 2008. ICSICT 2008. 9th International Conference on; 11/2008
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ABSTRACT: A cost-effective isolation technique using laser treatment is proposed to suppress the undesired crosstalk between dual power amplifiers (PAs), which are essential to multiple-input multiple-output communications system. Laser treatment not only reduces the small-signal coupling between dual PAs but also enhances the linearity of the PA under dual-PA operation mode. The figure of merit for the small-signal coupling has an improvement of 4.55 dB at 2.45 GHz, and the output power at 3% (- 30 dB) error vector magnitude (EVM) has a linearity improvement of 6.1 dB under 0-dB interference.
IEEE Microwave and Wireless Components Letters 10/2008; · 1.72 Impact Factor
