19 research outputs found
Transport properties and functional devices on CVD grown Silicon nanowires
My thesis is devoted to the study of transport properties of Silicon Nanowires obtained by a bottom-up approach. The choice for the material system has been limited to undoped SiNWs because they are considered as the ultimate choice for ultrascaled electronic devices. For these systems, the problem of an effective carrier injection in the semiconductor is particularly important. The mechanism of carrier injection in Gate-All-Around Schottky barrier transistors was studied by temperature dependent measurements. Multiple gates are used to discriminate between different device switching mechanisms occurring either at the source and drain contacts, or at the level of the silicon channel. The gating scheme has proved be effective in suppressing the Schottky barrier enabling carrier injection at low temperature. Moreover, different electronic functionalities like p-n junctions and logic gates can be successfully implemented in such devices without the need of doping. I will describe a novel technique for the fabrication of metal silicide contacts to individual silicon nanowires based on an electrically-controlled Joule annealing process. This has enabled the realization of silicide-silicon-silicide tunnel junctions with silicon channel lengths down to 8nm. The silicidation of silicon nanowires by Nickel and Platinum could be observed in-situ and in real time by performing the experiments of Joule assisted silicidation in the chamber of a Scanning Electron Microscope. Lastly, signatures of resonant tunneling through an isolated Platinum Silicide cluster were detected in a Silicon tunnel junction. Tunneling spectroscopy in a magnetic field revealed the Zeeman splitting of the ground and the excited states
PtSi Clustering In Silicon Probed by Transport Spectroscopy
Metal silicides formed by means of thermal annealing processes are employed
as contact materials in microelectronics. Control of the structure of
silicide/silicon interfaces becomes a critical issue when the device
characteristic size is reduced below a few tens of nanometers. Here we report
on silicide clustering occurring within the channel of PtSi/Si/PtSi Schottky
barrier transistors. This phenomenon is investigated through atomistic
simulations and low-temperature resonant tunneling spectroscopy. Our results
provide evidence for the segregation of a PtSi cluster with a diameter of a few
nanometers from the silicide contact. The cluster acts as metallic quantum dot
giving rise to distinct signatures of quantum transport through its discrete
energy states
Modelling semiconductor spin qubits and their charge noise environment for quantum gate fidelity estimation
The spin of an electron confined in semiconductor quantum dots is currently a
promising candidate for quantum bit (qubit) implementations. Taking advantage
of existing CMOS integration technologies, such devices can offer a platform
for large scale quantum computation. However, a quantum mechanical framework
bridging a device's physical design and operational parameters to the qubit
energy space is lacking. Furthermore, the spin to charge coupling introduced by
intrinsic or induced Spin-Orbit-Interaction (SOI) exposes the qubits to charge
noise compromising their coherence properties and inducing quantum gate errors.
We present here a co-modelling framework for double quantum dot (DQD) devices
and their charge noise environment. We use a combination of an electrostatic
potential solver, full configuration interaction quantum mechanical methods and
two-level-fluctuator models to study the quantum gate performance in realistic
device designs and operation conditions. We utilize the developed models
together alongside the single electron solutions of the quantum dots to
simulate one- and two- qubit gates in the presence of charge noise. We find an
inverse correlation between quantum gate errors and quantum dot confinement
frequencies. We calculate X-gate fidelities >97% in the simulated Si-MOS
devices at a typical TLF densities. We also find that exchange driven two-qubit
SWAP gates show higher sensitivity to charge noise with fidelities down to 91%
in the presence of the same density of TLFs. We further investigate the one-
and two- qubit gate fidelities at different TLF densities. We find that given
the small size of the quantum dots, sensitivity of a quantum gate to the
distance between the noise sources and the quantum dot creates a strong
variability in the quantum gate fidelities which can compromise the device
yields in scaled qubit technologies.Comment: 23 pages , 16 figure
Low charge noise quantum dots with industrial CMOS manufacturing
Silicon spin qubits are among the most promising candidates for large scale
quantum computers, due to their excellent coherence and compatibility with CMOS
technology for upscaling. Advanced industrial CMOS process flows allow
wafer-scale uniformity and high device yield, but off the shelf transistor
processes cannot be directly transferred to qubit structures due to the
different designs and operation conditions. To therefore leverage the know-how
of the micro-electronics industry, we customize a 300mm wafer fabrication line
for silicon MOS qubit integration. With careful optimization and engineering of
the MOS gate stack, we report stable and uniform quantum dot operation at the
Si/SiOx interface at milli-Kelvin temperature. We extract the charge noise in
different devices and under various operation conditions, demonstrating a
record-low average noise level of 0.61 eV/ at 1 Hz and even
below 0.1 eV/ for some devices and operating conditions. By
statistical analysis of the charge noise with different operation and device
parameters, we show that the noise source can indeed be well described by a
two-level fluctuator model. This reproducible low noise level, in combination
with uniform operation of our quantum dots, marks CMOS manufactured MOS spin
qubits as a mature and highly scalable platform for high fidelity qubits.Comment: 22 pages, 13 figure
Joule-assisted silicidation for short-channel silicon nanowire devices
We report on a technique enabling electrical control of the contact
silicidation process in silicon nanowire devices. Undoped silicon nanowires
were contacted by pairs of nickel electrodes and each contact was selectively
silicided by means of the Joule effect. By a realtime monitoring of the
nanowire electrical resistance during the contact silicidation process we were
able to fabricate nickel-silicide/silicon/nickel- silicide devices with
controlled silicon channel length down to 8 nm.Comment: 6 pages, 4 figure
Multifunctional Devices and Logic Gates With Undoped Silicon Nanowires
We report on the electronic transport properties of multiple-gate devices
fabricated from undoped silicon nanowires. Understanding and control of the
relevant transport mechanisms was achieved by means of local electrostatic
gating and temperature dependent measurements. The roles of the source/drain
contacts and of the silicon channel could be independently evaluated and tuned.
Wrap gates surrounding the silicide-silicon contact interfaces were proved to
be effective in inducing a full suppression of the contact Schottky barriers,
thereby enabling carrier injection down to liquid-helium temperature. By
independently tuning the effective Schottky barrier heights, a variety of
reconfigurable device functionalities could be obtained. In particular, the
same nanowire device could be configured to work as a Schottky barrier
transistor, a Schottky diode or a p-n diode with tunable polarities. This
versatility was eventually exploited to realize a NAND logic gate with gain
well above one.Comment: 6 pages, 5 figure
The Opa1-Dependent Mitochondrial Cristae Remodeling Pathway Controls Atrophic, Apoptotic and Ischemic Tissue Damage
SummaryMitochondrial morphological and ultrastructural changes occur during apoptosis and autophagy, but whether they are relevant in vivo for tissue response to damage is unclear. Here we investigate the role of the optic atrophy 1 (OPA1)-dependent cristae remodeling pathway in vivo and provide evidence that it regulates the response of multiple tissues to apoptotic, necrotic, and atrophic stimuli. Genetic inhibition of the cristae remodeling pathway in vivo does not affect development, but protects mice from denervation-induced muscular atrophy, ischemic heart and brain damage, as well as hepatocellular apoptosis. Mechanistically, OPA1-dependent mitochondrial cristae stabilization increases mitochondrial respiratory efficiency and blunts mitochondrial dysfunction, cytochrome c release, and reactive oxygen species production. Our results indicate that the OPA1-dependent cristae remodeling pathway is a fundamental, targetable determinant of tissue damage in vivo
Overcoming I/O bottleneck in superconducting quantum computing: multiplexed qubit control with ultra-low-power, base-temperature cryo-CMOS multiplexer
Large-scale superconducting quantum computing systems entail high-fidelity
control and readout of large numbers of qubits at millikelvin temperatures,
resulting in a massive input-output bottleneck. Cryo-electronics, based on
complementary metal-oxide-semiconductor (CMOS) technology, may offer a scalable
and versatile solution to overcome this bottleneck. However, detrimental
effects due to cross-coupling between the electronic and thermal noise
generated during cryo-electronics operation and the qubits need to be avoided.
Here we present an ultra-low power radio-frequency (RF) multiplexing
cryo-electronics solution operating below 15 mK that allows for control and
interfacing of superconducting qubits with minimal cross-coupling. We benchmark
its performance by interfacing it with a superconducting qubit and observe that
the qubit's relaxation times () are unaffected, while the coherence times
() are only minimally affected in both static and dynamic operation. Using
the multiplexer, single qubit gate fidelities above 99.9%, i.e., well above the
threshold for surface-code based quantum error-correction, can be achieved with
appropriate thermal filtering. In addition, we demonstrate the capability of
time-division-multiplexed qubit control by dynamically windowing calibrated
qubit control pulses. Our results show that cryo-CMOS multiplexers could be
used to significantly reduce the wiring resources for large-scale qubit device
characterization, large-scale quantum processor control and quantum error
correction protocols.Comment: 16+6 pages, 4+1+5 figures, 1 tabl
Transport properties and functional devices on CVD grown Silicon nanowires
My thesis is devoted to the study of transport properties of Silicon Nanowires obtained by a bottom-up approach. The choice for the material system has been limited to undoped SiNWs because they are considered as the ultimate choice for ultrascaled electronic devices. For these systems, the problem of an effective carrier injection in the semiconductor is particularly important. The mechanism of carrier injection in Gate-All-Around Schottky barrier transistors was studied by temperature dependent measurements. Multiple gates are used to discriminate between different device switching mechanisms occurring either at the source and drain contacts, or at the level of the silicon channel. The gating scheme has proved be effective in suppressing the Schottky barrier enabling carrier injection at low temperature. Moreover, different electronic functionalities like p-n junctions and logic gates can be successfully implemented in such devices without the need of doping. I will describe a novel technique for the fabrication of metal silicide contacts to individual silicon nanowires based on an electrically-controlled Joule annealing process. This has enabled the realization of silicide-silicon-silicide tunnel junctions with silicon channel lengths down to 8nm. The silicidation of silicon nanowires by Nickel and Platinum could be observed in-situ and in real time by performing the experiments of Joule assisted silicidation in the chamber of a Scanning Electron Microscope. Lastly, signatures of resonant tunneling through an isolated Platinum Silicide cluster were detected in a Silicon tunnel junction. Tunneling spectroscopy in a magnetic field revealed the Zeeman splitting of the ground and the excited states