GaN-based HEMTs on Low Resistivity Silicon Technology for Microwave Applications

This paper investigates the effect of insertion AlN spacer between the GaN channel and buffer in a sub-micron gate (0.3 μm) AlGaN/GaN HEMTs on a low-resistivity (LR) (σ < 10 Ω.cm) silicon substrates on RF performance. Enhancement in short circuit current gain (fT) and maximum frequency of oscillation (fMAX) was observed in the HEMT with a 1 nm AlN spacer, where (fT) and (fMAX) were increased from 47 GHz to 55 GHz and 79 GHz to 121 GHz, respectively. Small-signal-modelling analysis was carried out to study this improvement in performance. We found that the AlN interlayer played a crucial role in reducing the gate-source capacitance, Cgs, by 36 % and delay, τ, by 20 % under the gate, as a result of an increase in mobility and a reduction in trap-related effects

Effect Of AlN Spacer In The Layer Structure On High Rf Performance GaN-Based HEMTs On Low Resistivity Silicon At K-Band Application

AlGaN/GaN High Electron Mobility Transistors (HEMTs) grown on Si substrate are emerging as an attractive devices for many RF applications. This is due to lower circuits realization cost and multifunction chips integration. In this study we investigate the effect of AlN spacer between AlGaN and GaN of a sub-micron gate (0.3 μm) AlGaN/GaN and AlGaN/AlN/GaN HEMTs on a Low Resistivity LR Si substrates on RF performance. We have observed an enhancement in RF performance fT and fMAX in the HEMT with of AlN spacer; (fT) was increased from 47 GHz to 55 GHz and (fMAX) was increased from 79 GHz to 121 GHz. This enhancement in performance is mainly due to the increase in the mobility in the channel and confinement of the carriers reducing Cgs, and delay τ under the gate. We believe this is the first RF study of this type as previous studies were based on the effects of the DC characteristic of the devices [1]

Terahertz Monolithic Integrated Circuits (TMICs) Array Antenna Technology On GaN-on-Low Resistivity Silicon Substrates

In this paper, we have demonstrated a viable microstrip array patch antenna technology for the first time on GaN-on-low resistivity silicon (LR-Si) substrates (ρ <; 40 Ω.cm) at H-band frequencies (220-325 GHz). The developed technology is compatible with standard MMIC technology with no requirement for high temperature processes. To mitigate the losses presented by the substrate and to enhance the performance of the integrated array antenna at THz frequencies, the driven patch is shielded by silicon nitride and gold layer in addition to a layer of benzocyclobutene (BCB). The demonstrated 4×1 array integrated antenna showed a measured resonance frequency in agreement with our simulation at 0.27 THz; a measured S11 as low as -41 dB was obtained. A directivity, gain and radiation efficiency of 11.2 dB, 5.2 dB, and 20% respectively was observed from the 3D EM model for a 5 μm BCB inset. To the authors' knowledge, this is the first demonstration of a THz integrated microstrip array antenna for TMIC technology; this developed technology is promising for high performance III-V electronic material on low resistivity/high dielectric substrates

Terahertz Microstrip Elevated Stack Antenna Technology on GaN-on-Low Resistivity Silicon Substrates for TMIC

In this paper we demonstrate a THz microstrip stack antenna on GaN-on-low resistivity silicon substrates (ρ < 40 Ω.cm). To reduce losses caused by the substrate and to enhance performance of the integrated antenna at THz frequencies, the driven patch is shielded by silicon nitride and gold in addition to a layer of benzocyclobutene (BCB). A second circular patch is elevated in air using gold posts, making this design a stack configuration. The demonstrated antenna shows a measured resonance frequency in agreement with the modeling at 0.27 THz and a measured S11 as low as −18 dB was obtained. A directivity, gain and radiation efficiency of 8.3 dB, 3.4 dB, and 32% respectively was exhibited from the 3D EM model. To the authors' knowledge, this is the first demonstrated THz integrated microstrip stack antenna for TMIC (THz Monolithic Integrated Circuits) technology; the developed technology is suitable for high performance III-V material on low resistivity/high dielectric substrates

Passive Components Technology for THz-Monolithic Integrated Circuits (THz-MIC)

In this work, a viable passive components and transmission media technology is presented for THz-Monolithic Integrated Circuits (THz-MIC). The developed technology is based on shielded microstrip (S-MS) employing a standard monolithic microwave integrated circuit compatible process. The S-MS transmission media uses a 5-μm layer of benzocyclobutene (BCB) on shielded metalized ground plates avoiding any substrate coupling effects. An insertion loss of less than 3 dB/mm was achieved for frequencies up to 750 GHz. To prove the effectiveness of the technology, a variety of test structures, passive components and antennas have been design, fabricated and characterized. High Q performance was demonstrated making such technology a strong candidate for future THz-MIC technology for many applications such as radar, communications, imaging and sensing

Candidate gene markers for sperm quality and fertility in bulls

Fertility is one of the primary traits of reproduction in bulls. Decrease in fertility is a multifactorial condition and is verydifficult to diagnose. Among various causes genetic abnormality holds a major share. By identifying various genes that haveeffects on fertility the genetic cause behind subferility can be explored and also other non genetic factors can be identified.Advancement of molecular genetic tools now easily enables us to explore individual genes in animals. Identification of thesegenes will eventually lead to genome assembly and development of novel tools for analysing complex genetic traits. Thispaper gives a brief idea about the candidate genes for bull fertility, including genes encoding hormones and their receptors,proteins of the seminal plasma, proteins involved in spermatozoa-ovum binding and genes influencing sexual development.The chromosomal location and gene structure are described, based on the bovine genome assembly

Electrical Control of Dynamic Spin Splitting Induced by Exchange Interaction as Revealed by Time Resolved Kerr Rotation in a Degenerate Spin-Polarized Electron Gas

The manipulation of spin degree of freedom have been demonstrated in spin polarized electron plasma in a heterostructure by using exchange-interaction induced dynamic spin splitting rather than the Rashba and Dresselhaus types, as revealed by time resolved Kerr rotation. The measured spin splitting increases from 0.256meV to 0.559meV as the bias varies from -0.3V to -0.6V. Both the sign switch of Kerr signal and the phase reversal of Larmor precessions have been observed with biases, which all fit into the framework of exchange-interaction-induced spin splitting. The electrical control of it may provide a new effective scheme for manipulating spin-selected transport in spin FET-like devices.Comment: 8 pages, 3 figures ; added some discussion

Evolution of the POU1F1 transcription factor in mammals: rapid change of the alternatively-spliced β-domain

The POU1F1 (Pit-1) transcription factor is important in regulating expression of growth hormone, prolactin and TSH β-subunit, and controlling development of the anterior pituitary cells in which these hormones are produced. POU1F1 is a conserved protein comprising three main domains, an N-terminal transcription activation domain (TAD), a POU-specific domain and a C-terminal homeodomain. Within the TAD, a β-domain can be inserted by alternative splicing, giving an extended 'β-variant' with altered properties. Here sequence data from over 100 species were used to assess the variability of POU1F1 in mammals. This showed that the POU-specific domain and homeodomain are very strongly conserved, and that the TAD is somewhat less conserved, as are linker and hinge regions between these main domains. On the other hand, the β-domain is very variable, apparently evolving at a rate not significantly different from that expected for unconstrained, neutral evolution. In several species stop and/or frameshift mutations within the β domain would prevent expression of the β-variant as a functional protein. In most species expression of the β-variant is low (<5% of total POU1F1 expression). The rate of evolution of POU1F1 in mammals shows little variation, though the lineage leading to dog does show an episode of accelerated change. This comparative genomics study suggests that in most mammalian species POU1F1 variants produced by alternative splicing may have little physiological significance

Spin Dynamics in the Second Subband of a Quasi Two Dimensional System Studied in a Single Barrier Heterostructure by Time Resolved Kerr Rotation

By biasing a single barrier heterostructure with a 500nm-thick GaAs layer as the absorption layer, the spin dynamics for both of the first and second subband near the AlAs barrier are examined. We find that when simultaneously scanning the photon energy of both the probe and pump beams, a sign reversal of the Kerr rotation (KR) takes place as long as the probe photons break away the first subband and probe the second subband. This novel feature, while stemming from the exchange interaction, has been used to unambiguously distinguish the different spin dynamics ($T_2^{1*}$ and $T_2^{2*}$) for the first and second subbands under the different conditions by their KR signs (negative for $1^{st}$ and positive for $2^{nd}$). In the zero magnetic field, by scanning the wavelength towards the short wavelength, $T_2^{1*}$ decreases in accordance with the D'yakonov-Perel' (DP) spin decoherence mechanism. At 803nm, $T_2^{2*}$(450ps) becomes ten times longer than $T_2^{1*}$(50ps). However, the value of $T_2^{2*}$ at 803nm is roughly the same as the value of $T_2^{1*}$ at 815nm. A new feature has been disclosed at the wavelength of 811nm under the bias of -0.3V (807nm under the bias of -0.6V) that the spin coherence times ($T_2^{1*}$ and $T_2^{2*}$) and the effective $g^*$ factors ($|g^*(E1)|$ and $|g^*(E2)|$) all display a sudden change, due to the "resonant" spin exchange coupling between two spin opposite bands.Comment: 9pages, 3 figure

Dual barrier InAlN/AlGaN/GaN-on-silicon high-electron-mobility transistors with Pt and Ni based gate stacks

In this work, we report the performance of 3 μm gate length "dual barrier„ InAlN/AlGaN/GaN HEMTs on Si substrates with gate-drain contact separations in the range 4-26 μm. Devices with Pt and Ni based gates were studied and their leakage characteristics are compared. Maximum drain current IDS of 1 A/mm, maximum extrinsic transconductance gm ~203 mS/mm and on-resistance Ron 4.07 Ω mm for gate to drain distance LGD = 4 μm were achieved. Nearly ideal sub-threshold swing of 65.6 mV/dec was obtained for LGD = 14 μm. The use of Pt based gate metal stacks led to a two to three orders of magnitude gate leakage current decrease compared to Ni based gates. The influence of InAlN layer thickness on the transistor transfer characteristics is also discussed