8 research outputs found
How to solve problems in micro- and nanofabrication caused by the emission of electrons and charged metal atoms during e-beam evaporation
We discuss how the emission of electrons and ions during
electron-beam-induced physical vapor deposition can cause problems in micro-
and nanofabrication processes. After giving a short overview of different types
of radiation emitted from an electron-beam (e-beam) evaporator and how the
amount of radiation depends on different deposition parameters and conditions,
we highlight two phenomena in more detail: First, we discuss an unintentional
shadow evaporation beneath the undercut of a resist layer caused by the one
part of the metal vapor which got ionized by electron-impact ionization. These
ions first lead to an unintentional build-up of charges on the sample, which in
turn results in an electrostatic deflection of subsequently incoming ionized
metal atoms towards the undercut of the resist. Second, we show how low-energy
secondary electrons during the metallization process can cause cross-linking,
blisters, and bubbles in the respective resist layer used for defining micro-
and nanostructures in an e-beam lithography process. After the metal
deposition, the cross-linked resist may lead to significant problems in the
lift-off process and causes leftover residues on the device. We provide a
troubleshooting guide on how to minimize these effects, which e.g. includes the
correct alignment of the e-beam, the avoidance of contaminations in the
crucible and, most importantly, the installation of deflector electrodes within
the evaporation chamber.Comment: 13 pages, 7 figure
Si/SiGe QuBus for single electron information-processing devices with memory and micron-scale connectivity function
The connectivity within single carrier information-processing devices
requires transport and storage of single charge quanta. Our all-electrical
Si/SiGe shuttle device, called quantum bus (QuBus), spans a length of 10
m and is operated by only six simply-tunable voltage pulses. It
operates in conveyor-mode, i.e. the electron is adiabatically transported while
confined to a moving QD. We introduce a characterization method, called
shuttle-tomography, to benchmark the potential imperfections and local
shuttle-fidelity of the QuBus. The fidelity of the single-electron shuttle
across the full device and back (a total distance of 19 m) is
. Using the QuBus, we position and detect up to 34
electrons and initialize a register of 34 quantum dots with arbitrarily chosen
patterns of zero and single-electrons. The simple operation signals,
compatibility with industry fabrication and low spin-environment-interaction in
Si/SiGe, promises spin-conserving transport of spin qubits for quantum
connectivity in quantum computing architectures.Comment: 11 pages, 6 figure
Sensing dot with high output swing for scalable baseband readout of spin qubits
A key requirement for quantum computing, in particular for a scalable quantum
computing architecture, is a fast and high-fidelity qubit readout. For
semiconductor based qubits, one limiting factor is the output swing of the
charge sensor. We demonstrate GaAs and Si/SiGe asymmetric sensing dots (ASDs),
which exceed the response of a conventional charge sensing dot by more than ten
times, resulting in a boosted output swing of . This
substantially improved output signal is due to a device design with a strongly
decoupled drain reservoir from the sensor dot, mitigating negative feedback
effects of conventional sensors. The large output signal eases the use of very
low-power readout amplifiers in close proximity to the qubit and will thus
render true scalable qubit architectures with semiconductor based qubits
possible in the future.Comment: 8 pages, 7 figure
Tailoring potentials by simulation-aided design of gate layouts for spin qubit applications
Gate-layouts of spin qubit devices are commonly adapted from previous
successful devices. As qubit numbers and the device complexity increase,
modelling new device layouts and optimizing for yield and performance becomes
necessary. Simulation tools from advanced semiconductor industry need to be
adapted for smaller structure sizes and electron numbers. Here, we present a
general approach for electrostatically modelling new spin qubit device layouts,
considering gate voltages, heterostructures, reservoirs and an applied
source-drain bias. Exemplified by a specific potential, we study the influence
of each parameter. We verify our model by indirectly probing the potential
landscape of two design implementations through transport measurements. We use
the simulations to identify critical design areas and optimize for robustness
with regard to influence and resolution limits of the fabrication process.Comment: 10 pages, 6 figure
The SpinBus Architecture: Scaling Spin Qubits with Electron Shuttling
Quantum processor architectures must enable scaling to large qubit numbers
while providing two-dimensional qubit connectivity and exquisite operation
fidelities. For microwave-controlled semiconductor spin qubits, dense arrays
have made considerable progress, but are still limited in size by wiring
fan-out and exhibit significant crosstalk between qubits. To overcome these
limitations, we introduce the SpinBus architecture, which uses electron
shuttling to connect qubits and features low operating frequencies and enhanced
qubit coherence. Device simulations for all relevant operations in the Si/SiGe
platform validate the feasibility with established semiconductor patterning
technology and operation fidelities exceeding 99.9 %. Control using room
temperature instruments can plausibly support at least 144 qubits, but much
larger numbers are conceivable with cryogenic control circuits. Building on the
theoretical feasibility of high-fidelity spin-coherent electron shuttling as
key enabling factor, the SpinBus architecture may be the basis for a spin-based
quantum processor that meets the scalability requirements for practical quantum
computing.Comment: 15 pages, 9 figure
Position effects at the FGF8 locus are associated with femoral hypoplasia
Copy-number variations (CNVs) are a common cause of congenital limb malformations and are interpreted primarily on the basis of their effect on gene dosage. However, recent studies show that CNVs also influence the 3D genome chromatin organization. The functional interpretation of whether a phenotype is the result of gene dosage or a regulatory position effect remains challenging. Here, we report on two unrelated families with individuals affected by bilateral hypoplasia of the femoral bones, both harboring de novo duplications on chromosome 10q24.32. The ∼0.5 Mb duplications include FGF8, a key regulator of limb development and several limb enhancer elements. To functionally characterize these variants, we analyzed the local chromatin architecture in the affected individuals’ cells and re-engineered the duplications in mice by using CRISPR-Cas9 genome editing. We found that the duplications were associated with ectopic chromatin contacts and increased FGF8 expression. Transgenic mice carrying the heterozygous tandem duplication including Fgf8 exhibited proximal shortening of the limbs, resembling the human phenotype. To evaluate whether the phenotype was a result of gene dosage, we generated another transgenic mice line, carrying the duplication on one allele and a concurrent Fgf8 deletion on the other allele, as a control. Surprisingly, the same malformations were observed. Capture Hi-C experiments revealed ectopic interaction with the duplicated region and Fgf8, indicating a position effect. In summary, we show that duplications at the FGF8 locus are associated with femoral hypoplasia and that the phenotype is most likely the result of position effects altering FGF8 expression rather than gene dosage effects.M.S. and A.S.-S. were supported by the Polish National Science Centre (UMO-2016/23/N/NZ2/02362 to M.S. and UMO-2016/21/D/NZ5/00064 to A.S.-S.). A.S.-S. was also supported by the Polish National Science Centre scholarship for PhD students (UMO-2013/08/T/NZ2/00027). C.L. is supported by postdoctoral Beatriu de Pinós from Secretaria d’Universitats I Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya and by the Marie Sklodowska-Curie COFUND program from H2020 (2018-BP-00055). A.J. was supported by the Polish National Science Centre (UMO-2016/22/E/NZ5/00270) as well as the Polish National Centre for Research and Development (LIDER/008/431/L-4/12/NCBR/2013). M.S. is supported by grants from the Deutsche Forschungsgemeinschaft (DFG) (SP1532/3-1, SP1532/4-1, and SP1532/5-1), the Max Planck Foundation, and the Deutsches Zentrum für Luft- und Raumfahrt (DLR 01GM1925)