29 research outputs found
Technology for satellite power conversion
Components were examined that will be needed for high frequency rectenna devices. The majority of the effort was spent on measuring the directivity and efficiency of the half-wave dipole antenna. It is felt that the antenna and diode should be roughly optimized before they are combined into a rectenna structure. An integrated low pass filter had to be added to the antenna structure in order to facilitate the field pattern measurements. A calculation was also made of the power density of the Earth's radiant energy as seen by satellites in Earth orbit. Finally, the feasibility of using a Metal-Oxide-Metal (MOM) diode for rectification of the received power was assessed
Technology for satellite power conversion
The work is this reporting period was concentrated on electronically calibrating the bolometer detectors. The calibration is necessary for two reasons: first, the power delivered to the rectifying circuit must be known in order to choose a diode with the appropriate barrier height, and second, the power captured by the antenna must be measured if the efficiency of the rectenna is to be divided into antenna efficiency and rectification efficiency. The millimeter wave region operation of the bolometers was simulated with a VHF (10 to 90 MHz) test signal. These detectors are accurate to within roughly 10%. The typical responsivity of the bolometers is 10 volts/watt and the NEP at 20 Hz is 5 times 10 to the minus 9th power W(Hz)-1/2
Technology for satellite power conversion
The work performed in this reporting period has concentrated on the metal-oxide-metal (MOM) diode. The fabrication procedure begins with the deposition of gold probing pads to provide a non-oxidizing contact to test the dc characteristics to the diode accurately. A thin patch capped with an insulating SiO2 layer, is deposited next to form the first half of the diode. The other half of the diode, typically Ni, is deposited completing the conduction path from the oxidized edge of the Ni patch to the opposite gold probing pad. It is important in this step that the last metallization take place without exposing the newly oxidized surface to the atmosphere. Successful production of diodes has been achieved. Work on millimeter wave frequency rectennas incorporating known semiconductor diode technology has been initiated
Infrared technology for satellite power conversion
Successful fabrication of bismuth bolometers led to the observation of antenna action rom array elements. Fabrication of the best antennas arrays was made more facile with finding that increased argon flow during the dc sputtering produced more uniform bismuth films and bonding to antennas must be done with the substrate temperaure below 100 C. Higher temperatures damaged the bolometers. During the testing of the antennas, it was found that the use of a quasi-optical system provided a uniform radiation field. Groups of antennas were bonded in series and in parallel with the parallel configuration showing the greater response
Technology for satellite power conversion
The dipole pattern of the antenna was confirmed and work on the MOM diode began. The antenna - detector structure was modified and the measurement apparatus reconfigured to permit precise antenna pattern measurements. Fabrication of the MOM diode was initiated after antenna action from the new structures was observed. A refined antenna structure was developed. The previous antenna design allowed currents induced by the incident radiation in the bonding wires to flow through the bolometer. The detector was thus responding to both the antenna and bonding wire currents. A low pass filter was added to the antenna structure to improve the detection scheme. The new design uses an interdigitated capacitor to prevent the induced current in the bonding wires from flowing through the detection element
Advanced Fabrication Processes for Superconducting Very Large Scale Integrated Circuits
We review the salient features of two advanced nodes of an 8-Nb-layer fully
planarized process developed recently at MIT Lincoln Laboratory for fabricating
Single Flux Quantum(SFQ) digital circuits with very large scale integration on
200-mm wafers: the SFQ4ee and SFQ5ee nodes, where 'ee' denotes the process is
tuned for energy efficient SFQ circuits. The former has eight superconducting
layers with 0.5 {\mu}m minimum feature size and a 2 {\Omega}/sq Mo layer for
circuit resistors. The latter has nine superconducting layers: eight Nb wiring
layers with the minimum feature size of 350 nm and a thin superconducting MoNx
layer (Tc ~ 7.5 K) with high kinetic inductance (about 8 pH/sq) for forming
compact inductors. A nonsuperconducting (Tc < 2 K) MoNx layer with lower
nitrogen content is used for 6 {\Omega}/sq planar resistors for shunting and
biasing of Josephson junctions. Another resistive layer is added to form
interlayer, sandwich-type resistors of m{\Omega} range for releasing unwanted
flux quanta from superconducting loops of logic cells. Both process nodes use
Au/Pt/Ti contact metallization for chip packaging. The technology utilizes one
layer of Nb/AlOx-Al/Nb JJs with critical current density, Jc of 100
{\mu}A/{\mu}m^2 and minimum diameter of 700 nm. Circuit patterns are defined by
248-nm photolithography and high density plasma etching. All circuit layers are
fully planarized using chemical mechanical planarization (CMP) of SiO2
interlayer dielectric. The following results and topics are presented and
discussed: the effect of surface topography under the JJs on the their
properties and repeatability, critical current and Jc targeting, effect of
hydrogen dissolved in Nb, MoNx properties for the resistor layer and for high
kinetic inductance layer, technology of m{\Omega}-range resistors.Comment: 10 pages, 12 figures, 1 table, 27 references. The paper was presented
on September 8, 2015 at the 12th European Conference on Applied
Superconductivity, EUCAS 2015, 6-10 September 2015, Lyon, France, IEEE
Transaction on Applied Superconductivity, 201
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Characterization of a large sex determination region in Salix purpurea L. (Salicaceae).
Dioecy has evolved numerous times in plants, but heteromorphic sex chromosomes are apparently rare. Sex determination has been studied in multiple Salix and Populus (Salicaceae) species, and P. trichocarpa has an XY sex determination system on chromosome 19, while S. suchowensis and S. viminalis have a ZW system on chromosome 15. Here we use whole genome sequencing coupled with quantitative trait locus mapping and a genome-wide association study to characterize the genomic composition of the non-recombining portion of the sex determination region. We demonstrate that Salix purpurea also has a ZW system on chromosome 15. The sex determination region has reduced recombination, high structural polymorphism, an abundance of transposable elements, and contains genes that are involved in sex expression in other plants. We also show that chromosome 19 contains sex-associated markers in this S. purpurea assembly, along with other autosomes. This raises the intriguing possibility of a translocation of the sex determination region within the Salicaceae lineage, suggesting a common evolutionary origin of the Populus and Salix sex determination loci
Progress toward superconductor electronics fabrication process with planarized NbN and NbN/Nb layers
To increase density of superconductor digital and neuromorphic circuits by
10x and reach integration scale of Josephson junctions (JJs) per chip,
we developed a new fabrication process on 200-mm wafers, using self-shunted
Nb/Al-AlOx/Nb JJs and kinetic inductors. The process has a layer of JJs, a
layer of resistors, and 10 fully planarized superconducting layers: 8 Nb layers
and 2 layers of high kinetic inductance materials, MoN and NbN, with sheet
inductance of 8 pH/sq and 3 pH/sq, respectively. NbN films were deposited by
two methods: with =15.5 K by reactive sputtering of a Nb target in
Ar+N mixture; with in the range from 9 K to 13 K by plasma-enhanced
chemical vapor deposition (PECVD) using
Tris(diethylamido)(tert-butylimido)niobium(V) metalorganic precursor. PECVD of
NbN was investigated to obtain conformal deposition and filling narrow trenches
and vias with high depth-to-width ratios, which was not possible to achieve
using sputtering and other physical vapor deposition (PVD) methods at
temperatures below required to prevent degradation of Nb/Al-AlOx/Nb
junctions. Nb layers with 200 nm thickness are used in the process layer stack
as ground planes to maintain a high level of interlayer shielding and low
intralayer mutual coupling, for passive transmission lines with wave impedances
matching impedances of JJs, typically <=50 , and for low-value
inductors. NbN and NbN/Nb bilayer are used for cell inductors. Using NbN/Nb
bilayers and individual pattering of both layers to form inductors allowed us
to minimize parasitic kinetic inductance associated with interlayer vias and
connections to JJs as well as to increase critical currents of the vias.
Fabrication details and results of electrical characterization of NbN films,
wires, and vias, and comparison with Nb properties are given.Comment: 12 pages, 16 figures, 4 tables, 49 references. Submitted to IEEE TAS
on Nov. 10, 202