Bias Swing Research Articles

Characterizing third-order intermodulation distortion of photodetectors based on de-coupling and de-embedding modulation distortion of modulators

A novel, to the best of our knowledge, electro-optical modulation method is proposed for measuring third-order intermodulation distortion of photodetectors (PDs) based on de-coupling and de-embedding modulation distortion of modulators. The method utilizes dual parallel intensity modulation to generate electro-optical stimulus signals with fast and fine sweeping capability, and it eliminates the nonlinear impact of modulators by using low-frequency bias swing, allowing a direct extraction of the third-order output intercept point (OIP3) of PD from the combined nonlinear response contributed by both the modulators and the PD. The OIP3 of PD is frequency-swept measured with our method and compared to those with the conventional method to check for consistency. The proposed method enables a modulator-distortion-free, fast, and fine sweeping measurement of PDs using a simple system.

Self-referenced electro-optic response measurement of dual-parallel Mach-Zehnder modulators employing single-tone level control and low-frequency bias swing.

A self-referenced method is proposed to characterize the electro-optic frequency response of dual-parallel Mach-Zehnder modulators (DPMZMs) based on single-tone level control and low-frequency bias swing. The single-tone driving signal and the low-frequency bias signal of the DPMZM mix with each other after photodetection, and a low-frequency beat note is generated in the electrical domain. The functional relationship between the desired low-frequency amplitude and the single-tone driving level is investigated and established, from which the modulation depth and half-wave voltage are extracted with the help of regression analysis. We experimentally demonstrate the feasibility of the proposed method and compare it with the conventional ones to check the consistency. The self-referenced method features single-tone modulation and low-frequency detection for measuring high-speed DPMZMs, which avoids the use of a broadband photodetector (PD) and the influence of the uneven response of the PD.

(Invited) Vertical Tunnel FET Technologies Using III-V/Si Heterojunction

Millivolt switches based on non-thermionic transport mechanism must demonstrate a steep slope (small gate bias swing), moderate conductance, high efficiency, and rational integration scheme including high density with complementary operation toward low-power integrated circuits. Because these inherent requirements can be satisfied by a vertical III-V nanowire (NW) channel with a surrounding-gate structure and a heterojunction underneath the NWs. Here we report on vertical tunnel field-effect transistor (TFET) technologies using III-V nanowire/Si heterojunctions.

Recent Progress on Ge/SiGe Quantum Well Optical Modulators, Detectors, and Emitters for Optical Interconnects

Germanium/Silicon-Germanium (Ge/SiGe) multiple quantum wells receive great attention for the realization of Si-based optical modulators, photodetectors, and light emitters for short distance optical interconnects on Si chips. Ge quantum wells incorporated between SiGe barriers, allowing a strong electro-absorption mechanism of the quantum-confined Stark effect (QCSE) within telecommunication wavelengths. In this review, we respectively discuss the current state of knowledge and progress of developing optical modulators, photodetectors, and emitters based on Ge/SiGe quantum wells. Key performance parameters, including extinction ratio, optical loss, swing bias voltages, and electric fields, and modulation bandwidth for optical modulators, dark currents, and optical responsivities for photodetectors, and emission characteristics of the structures will be presented.

Human parthenogenetic neural stem cell grafts promote multiple regenerative processes in a traumatic brain injury model.

International Stem Cell Corporation human parthenogenetic neural stem cells (ISC-hpNSC) have potential therapeutic value for patients suffering from traumatic brain injury (TBI). Here, we demonstrate the behavioral and histological effects of transplanting ISC-hpNSC intracerebrally in an animal model of TBI.Methods: Sprague-Dawley rats underwent a moderate controlled cortical impact TBI surgery. Transplantation occurred at 72 h post-TBI with functional readouts of behavioral and histological deficits conducted during the subsequent 3-month period after TBI. We characterized locomotor, neurological, and cognitive performance at baseline (before TBI), then on days 0, 1, 7, 14, 30, 60, and 90 (locomotor and neurological), and on days 28-30, 58-60, and 88-90 (cognitive) after TBI. Following completion of behavioral testing at 3 months post-TBI, animals were euthanized by transcardial perfusion and brains harvested to histologically characterize the extent of brain damage. Neuronal survival was revealed by Nissl staining, and stem cell engraftment and host tissue repair mechanisms such as the anti-inflammatory response in peri-TBI lesion areas were examined by immunohistochemical analyses.Results: We observed that TBI groups given high and moderate doses of ISC-hpNSC had an improved swing bias on an elevated body swing test for motor function, increased scores on forelimb akinesia and paw grasp neurological tests, and committed significantly fewer errors on a radial arm water maze test for cognition. Furthermore, histological analyses indicated that high and moderate doses of stem cells increased the expression of phenotypic markers related to the neural lineage and myelination and decreased reactive gliosis and inflammation in the brain, increased neuronal survival in the peri-impact area of the cortex, and decreased inflammation in the spleen at 90 days post-TBI.Conclusion: These results provide evidence that high and moderate doses of ISC-hpNSC ameliorate TBI-associated histological alterations and motor, neurological, and cognitive deficits.

Abstract WMP77: Anti-Inflammatory Signaling by Leukemia Inhibitory Factor is Suppressed in Aged Animals After Stroke

Objective: To determine whether the anti-inflammatory effects of leukemia inhibitory factor (LIF) are altered in aged male and female rats. Methods: Focal ischemia was induced in 3 month old male and 18 month old male/female Sprague-Dawley using the middle cerebral artery occlusion (MCAO) procedure. Animals were treated with PBS or LIF at 6, 24, and 48 h after MCAO (125 μg/kg). Infarct volume in aged animals was quantified with T2-weighted MRI. Functional motor skills were assessed immediately prior to euthanization at 72 h post-MCAO. Protein levels of CD11b and IL-12 p40 in brain and spleen tissue were measured using immunoblotting. Results: At 72 h, there was a trend towards decreased infarct volume in aged male (189 ± 45OD; n=4) and female LIF-treated rats (104 ± 71 OD; n=4) compared to PBS-treated aged male (188 ± 45; n=4) and female rats (179 ± 72; n=5). LIF-treated aged female rats showed significant decreases in circling (p=0.0209) and body swing bias (p=0.05) compared to the PBS-treated aged females. Normalized CD11b levels were significantly in LIF-treated young males (1.1 ± 0.3 OD; n=5) compared to PBS-treated young males (2.5 ± 0.5 OD; n=6; p<0.05). Although aged male (1.2 ± 0.4 OD) and females (1.2 ± 0.3 OD) had lower levels of CD11b in the brain 72 h post-MCAO compared to young males, LIF had no effect on brain CD11b levels in aged rats. LIF increased spleen size (1.6 ± 0.1 g) and splenic CD11b levels (0.11 ± 0.01 OD) compared to PBS-treated females (0.6 ± 0.1 g; 0.08 ± 0.01 OD; p<0.05), and there was a significant positive correlation between these two factors in the aged female rats (r = 0.6775; p<0.05). Furthermore, IL-12 p40 levels in splenic tissue were significantly higher in young male PBS-treated rats (0.38 ± 0.06 OD) compared to aged male (0.12 ± 0.01 OD; p<0.01) and female rats (0.16 ± 0.04 OD; p<0.01). LIF treatment reduced IL-12 p40 levels in the spleen in young rats (0.24 ± 0.04; p<0.05) but not in either of the aged rat groups. Conclusions: LIF is more effective at decreasing splenic IL-12 expression and immune cell infiltration in young rats compared to aged rats. However, LIF counteracts the post-stroke splenic response in aged females but not aged male rats.

Selective Area Growth: A Promising Way for Recessed Gate GaN MOSFET With High Quality MOS Interface

Based on the selective area growth (SAG) technique, an enhancement mode GaN recessed gate MOSFET was fabricated successfully with negligible gate trapping effect, presenting an extremely small threshold voltage ( $V_{\mathrm {th}})$ hysteresis of 50 mV at a gate bias swing up to 10 V. Compared with the larger $V_{\mathrm {th}}$ hysteresis of a recessed gate GaN MOSFET fabricated by dry-etching, the correlation between the $V_{\mathrm {th}}$ hysteresis and the lattice damage related traps caused by plasma dry etching process has been confirmed. Furthermore, the SAG recessed MOSFET shows a lower turn-ON resistance due to the higher MOS channel mobility. We believe that all of these superior performance of SAG MOSFET are attributed to the damage free high quality GaN surface at the Al2O3/GaN MOS interface, which indicates that the SAG is a promising alternative technique toward stable GaN MOSFET for the power switching applications.

Electrografted Fluorinated Organic Ultrathin Film as Efficient Gate Dielectric in MoS2 Transistors

Dielectric films with nanometer thickness play a central role in the performances of field effect transistors (FETs). In this article, a new class of organic gate dielectric based on the electrochemical grafting of diazonium salts on metallic electrodes is investigated. The versatile diazonium salt strategy is a local and room-temperature process that provides robustness and performances. Moreover, this process produces ultrathin (4–8 nm) and smooth films. To prove their efficiency as gate dielectric, they were integrated in MoS2–FETs gate stacks. The devices display excellent switching behavior for reduced gate bias swing (down to 1 V) and suppressed hysteresis thanks to the highly hydrophobic nature of the fluorinated grafted film. Furthermore, the devices exhibit steep subthreshold slopes (as low as 110 mV/decade), demonstrating excellent gate coupling.

Proposed ultralow-energy dual photonic-crystal nanobeam devices for on-chip N x N switching, logic, and wavelength multiplexing.

Silicon-on-insulator Mach-Zehnder interferometer structures that utilize a photonic crystal nanobeam waveguide in each of two connecting arms are proposed here as efficient 2 × 2 resonant, wavelength-selective electro-optical routing switches that are readily cascaded into on-chip N × N switching networks. A localized lateral PN junction of length ~2 μm within each of two identical nanobeams is proposed as a means of shifting the transmission resonance by 400 pm within the 1550 nm band. Using a bias swing ΔV = 2.7 V, the 474 attojoules-per-bit switching mechanism is free-carrier sweepout due to PN depletion layer widening. Simulations of the 2 × 2 outputs versus voltage are presented. Dual-nanobeam designs are given for N × N data-routing matrix switches, electrooptical logic unit cells, N × M wavelength selective switches, and vector matrix multipliers. Performance penalties are analyzed for possible fabrication induced errors such as non-ideal 3-dB couplers, differences in optical path lengths, and variations in photonic crystal cavity resonances.

A coplanar waveguide bandwidth-tunable lowpass filter with broadband rejection

A coplanar waveguide lowpass filter (CPW-LPF) with high bandwidth tunability and broadband rejection is demonstrated. Compared to the reported design approaches, a relatively straightforward design with varactor-tuned microwave resonators is proposed for the realization of the tunable CPW-LPF. It is shown that the presented tunable CPW-LPF has a wide bandwidth tuning range via a small bias swing, low passband insertion loss, as well as wideband rejection. Also, the filter roll-off remains unchanged while the cut-off frequency is varied. The proposed tunable CPW-LPF is experimentally verified and expected to find applications in modern communication systems.

Ge quantum well optoelectronic devices for light modulation, detection, and emission

We report on light modulation, detection, and emission characteristics of Ge/SiGe multiple quantum well waveguides using the same epitaxial growth and fabrication steps. As an electro-absorption modulator, the device exhibits the capability to achieve high extinction ratio with low swing bias voltages and high modulation bandwidth. As a photodetector, dark currents, optical responsivities, and high speed performance have been studied. High speed light detection up to 10Gb/s has been obtained simultaneously with good values of optical responsivity. As a light emitting diode, direct gap electroluminescence (EL) from the Ge/SiGe MQW waveguides has been experimentally demonstrated at room temperature within the spectral range of light modulation and detection.

CMOS Process-Compatible High-Power Low-Leakage AlGaN/GaN MISHEMT on Silicon

We report on a novel Au-free CMOS process-compatible process for AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors. The process starts from a 150-mm GaN-on-Si substrate with an embedded Si3N4/Al2O3 bilayer gate dielectric, encapsulated by a high-temperature low-pressure chemical vapor deposited nitride layer. Power devices with a 20-mm gate width reach a maximum output current of 8 A, a breakdown voltage of 750 V, and a specific on-resistance Ron, sp of 2.9 mΩ·cm2. The off-state drain leakage at 600 V is 7 μA. We show robust gate dielectrics with a large gate bias swing.

Injectable VEGF Hydrogels Produce Near Complete Neurological and Anatomical Protection following Cerebral Ischemia in Rats

Vascular endothelial growth factor (VEGF) is a potent proangiogenic peptide and its administration has been considered as a potential neuroprotective strategy following cerebral stroke. Because VEGF has a short half-life and limited access to the brain parenchyma following systemic administration, approaches are being developed to deliver it directly to the site of infarction. In the present study, VEGF was incorporated into a sustained release hydrogel delivery system to examine its potential benefits in a rat model of cerebral ischemia. The hydrogel loaded with VEGF (1 μg) was stereotaxically injected into the striatum of adult rats 15 min prior to a 1-h occlusion of the middle cerebral artery. Two days after surgery, animals were tested for motor function using the elevated bias swing test (EBST) and Bederson neurological battery. Control animals received either stroke alone, stroke plus injections of a blank gel, or a single bolus injection of VEGF (1 μg). Behavioral testing confirmed that the MCA occlusion resulted in significant deficits in the the EBST and Bederson tests. In contrast, the performance of animals receiving VEGF gels was significantly improved relative to controls, with only modest impairments observed. Cerebral infarction analyzed using 2,3,5-triphenyl-tetrazolium chloride staining confirmed that the VEGF gels significantly and potently reduced the lesion volume. No neurological or histological benefits were conferred by either blank gel or bolus VEGF injections. These data demonstrate that VEGF, delivered from a hydrogel directly to the brain, can induce significant functional and structural protection from ischemic damage in a rat model of stroke.

Sub‐100 nm gate‐length SiGe/Si MIS‐HFET using Cat‐CVD SiN

AbstractWe fabricated sub‐100 nm gate‐length SiGe/Si n‐channel metal‐insulator‐semiconductor (MIS) heterostructure field‐effect transistors (HFETs) using a SiN gate insulator formed by catalytic chemical vapor deposition (Cat‐CVD). The Cat‐CVD SiN thin film (5 nm) was found to be an effective gate insulator with good gate controllability and dielectric properties. Due to the MIS structure, large gate bias swing was achieved from ‐3 to 3 V, and the maximum drain current density exceeded 450 mA/mm. The maximum transconductance (gm) was 220 mS/mm at VGS = 3 V, which was larger than that for a Schottky‐gate device. RF measurements of the MIS‐gate device, however, showed a relatively lower current gain cutoff frequency (fT) compared with the Schottky‐gate device, suggesting that two electron transport channels existed for the MIS‐gate structure, one at the SiGe/Si buried channel and the other at the SiN/Si surface channel. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Evaluation of AlGaN/GaN‐HFET with HfAlO gate insulator

AbstractMetal‐insulator‐semiconductor (MIS) heterostructure field‐effect transistors (HFETs) fabricated with HfAlO as a gate insulator with high dielectric permittivity are demonstrated to achieve true enhancement‐mode operation with no gate leakage and high drain current density. Insertion of the HfAlO layer allows for forward gate bias voltages of up to +8 V without gate leakage (maximum gate current density of 1.2×10–5 mA/mm at +8 V gate bias) under direct current operation. Utilizing the extended forward gate bias swing, a maximum drain current density of 767 mA/mm is achieved, substantially higher than that of the non‐insulated HFET (427 mA/mm). A recessed‐gate MIS‐HFET with the HfAlO gate insulator exhibits a threshold voltage of +2.0 V and zero transconductance below a gate bias of +0.9 V, demonstrating true enhancement‐mode operation for the first time in recessed‐gate AlGaN/GaN‐HFETs with a maximum drain current density of 253 mA/mm at +5 V (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Blue quantum electroabsorption modulators based on reversed quantum confined Stark effect with blueshift

The authors present the design, growth, fabrication, experimental characterization, and theoretical analysis of blue quantum electroabsorption modulators that incorporate ∼5nm thick In0.35Ga0.65N∕GaN quantum structures for operation between 420 and 430nm. Growing on polar c plane on sapphire, they obtain quantum structures with zigzag potential profile due to alternating polarization fields and demonstrate that their optical absorption blueshifts with applied electric field, unlike the redshift of conventional quantum confined Stark effect. In InGaN∕GaN quantum structures, they report the largest absorption change of 6000cm−1 for 6V bias swing around 424nm, holding promise for blue optical clock generation and injection directly into silicon chips.

Comparative studies on the stability of polymer versus SiO2 gate dielectrics for pentacene thin-film transistors

The authors report on the electrical reliabilities of poly-4-vinyl phenol (PVP) and SiO2 gate dielectrics for pentacene thin-film transistors (TFTs). SiO2 films were grown by dry oxidation and PVP films were prepared by spin coating and subsequent cross-linking at 175°C for 15min. The pentacene TFTs with the PVP cured for 15min exhibited a large hysteresis and an abnormal drain-current increase under a gate bias stress over time, while the other TFT with SiO2 displayed a small hysteresis but its drain current decreases with time. The hysteresis behaviors induced by PVP and SiO2 were opposite to each other in the gate bias swing direction, due to the difference in hysteresis mechanism between the two types of TFTs. Comparing their hysteresis behavior, the authors fabricated a far more reliable pentacene TFT with PVP by extending the PVP curing time to 1h. Our improved device with PVP exhibited no hysteresis and persistent toughness to the gate bias stress.

Behavioral differences in a rotenone-induced hemiparkinsonian rat model developed following intranigral or median forebrain bundle infusion

A mitochondrial complex-I inhibitor, rotenone was unilaterally infused into the substantia nigra pars compacta (SNpc) or median forebrain bundle (MFB) to create hemiparkinsonian animal models and investigated spontaneous and drug-induced stereotypic rotations, as well as certain postural behaviors in Sprague–Dawley rats. Animals infused intranigrally, but not intra-MFB, with rotenone exhibited spontaneous contralateral rotations immediately after recovery from anesthesia. Head position bias and elevated body swing test showed insignificant contralateral bias in animals with nigral damage but a significant ipsilateral bias in MFB-lesioned rats. General motor activity of the animals was reduced in both the groups as indicated by reduced performance on a Plus-Maze. Intranigrally, rotenone-infused animals exhibited progressive ipsilateral rotations when challenged with d-amphetamine on the 7th, 14th, 21st, and 28th days or with apomorphine on 9th, 16th, 23rd, and 30th days. However, animals that received rotenone in MFB exhibited ipsilateral or contralateral rotations when challenged respectively with d-amphetamine or apomorphine only in the 5th week (28th and 30th days). Stereotaxic administration of rotenone into SNpc or MFB caused a significant loss of dopamine in the ipsilateral striatum (>80% in SNpc; >95% in MFB), when assayed employing an HPLC equipped with electrochemical detector on the 32nd day. Neuronal loss in SNpc was confirmed in coronal sections stained with cresyl violet and revealed extension of lesion towards SN pars reticulata, in SNpc-infused animals. Our results demonstrate that rotenone-induced neurodegeneration is a slow, yet progressive process similar to that in idiopathic Parkinson's disease and unlike that observed in other classical neurotoxin-mediated lesions which are abrupt and developed in few hours to days. Thus, intranigral or intra-MFB infusion of rotenone could be used for producing hemiparkinsonian animal models in rats. These findings further suggest that, while both d-amphetamine and apomorphine-induced stereotypic rotations could be used as a valuable behavioral assay procedure to test novel drugs against Parkinson's disease, yet apomorpine-induced contralateral bias in turning is a reliable indicator of specific destruction in nigrostriatal pathway and development of postsynaptic dopamine receptor supersensitivity.

High-quality HfSixOy gate dielectrics fabricated by solid phase interface reaction between physical-vapor-deposited metal–Hf and SiO2 underlayer

We fabricated high-quality Hf–silicate (HfSixOy) gate dielectrics by utilizing the solid phase interface reaction between physical-vapor-deposited metal–Hf (typically 0.5nm thick) and SiO2 underlayers. Metal diffusion to the SiO2 layer increases the permittivity of the underlayer, while preservation of the initial SiO2∕Si bottom interface ensures good electrical properties of the gate dielectrics. The Hf–silicate layer remains amorphous and the poly-Si∕HfSixOy gate stack endures activation annealing at 1000°C. The interface trap density was comparable to that of conventional SiO2 dielectrics and the hysteresis of capacitance–voltage curves was as low as 4mV for a bias swing between −2 and +2.5V. Moreover, high electron mobility, equal to 89% of the universal mobility, was obtained for the high-k gate transistor.

Design and characterization of AlGaAs/InGaAs/GaAs-based double-heterojunction PHEMT device

We report on the design and characterization of pseudomorphic high-electron-mobility transistors for linear power applications. Compared to a conventional single heterojunction, the double-heterojunction PHEMT shows a flat transconductance of >200 mS/mm over a wide gate bias swing. A high breakdown voltage of 15 V was measured. A flat cutoff frequency (fT) of >15 GHz over a wide gate and drain bias region was achieved. A maximum oscillation frequency (fmax) of >75 GHz was obtained. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 50–53, 1998.