The exceptionally long quantum coherence times of phosphorus donor nuclear spin qubits in silicon, coupled with the proven scalability of silicon-based nano-electronics, make them attractive candidates for large-scale quantum computing. However, the high threshold of topological quantum error correction can only be captured in a two-dimensional array of qubits operating synchronously and in parallel—posing formidable fabrication and control challenges. We present an architecture that addresses these problems through a novel shared-control paradigm that is particularly suited to the natural uniformity of the phosphorus donor nuclear spin qubit states and electronic confinement. The architecture comprises a two-dimensional lattice of donor qubits sandwiched between two vertically separated control layers forming a mutually perpendicular crisscross gate array. Shared-control lines facilitate loading/unloading of single electrons to specific donors, thereby activating multiple qubits in parallel across the array on which the required operations for surface code quantum error correction are carried out by global spin control. The complexities of independent qubit control, wave function engineering, and ad hoc quantum interconnects are explicitly avoided. With many of the basic elements of fabrication and control based on demonstrated techniques and with simulated quantum operation below the surface code error threshold, the architecture represents a new pathway for large-scale quantum information processing in silicon and potentially in other qubit systems where uniformity can be exploited.

https://advances.sciencemag.org/content/advances/1/9/e1500707.full.pdf

A surface code quantum computer in silicon

We present designs, theory, and results of fabrication and testing for a novel parallel microrobotic assembly scheme using stress-engineered MEMS microrobots. The robots are 240-280 mum times 60 mum times 7-20 mum in size and can be controlled to dock compliantly together, forming planar structures several times this size. The devices are classified into species based on the design of their steering arm actuators, and the species are further classified as independent if they can be maneuvered independently using a single global control signal. In this paper, we show that microrobot species are independent if the two transition voltages of their steering arms, i.e., the voltages at which the arms are raised or lowered, form a unique pair. We present control algorithms that can be applied to groups of independent microrobot species to direct their motion from arbitrary nondead-lock configurations to desired planar microassemblies. We present designs and fabrication for four independent microrobot species, each with a unique transition voltage. The fabricated microrobots are used to demonstrate directed assembly of five types of planar structures from two classes of initial conditions. We demonstrate an average docking accuracy of 5 mum and use self-aligning compliant interaction between the microrobots to further align and stabilize the intermediate assemblies. The final assemblies match their target shapes on average 96%, by area.

/pdf/planar-microassembly-by-parallel-actuation-of-mems-4ma5n04u4j.pdf

Planar Microassembly by Parallel Actuation of MEMS Microrobots

A defining feature of modern CMOS devices and almost all quantum semiconductor devices is the use of many different materials. For example, although electrical conduction often occurs in single-crystal semiconductors, gates are frequently made of metals and dielectrics are commonly amorphous. Such devices have demonstrated remarkable improvements in performance over recent decades, but the heterogeneous nature of these devices can lead to defects at the interfaces between the different materials, which is a disadvantage for applications in spintronics and quantum information processing. Here we report the fabrication of a few-electron quantum dot in single-crystal silicon that does not contain any heterogeneous interfaces. The quantum dot is defined by atomically abrupt changes in the density of phosphorus dopant atoms, and the resulting confinement produces novel effects associated with energy splitting between the conduction band valleys. These single-crystal devices offer the opportunity to study how very sharp, atomic-scale confinement--which will become increasingly important for both classical and quantum devices--influences the operation and performance of devices.

/pdf/spectroscopy-of-a-few-electron-single-crystal-silicon-132ob2bds0.pdf

Spectroscopy of a few-electron single-crystal silicon quantum dot

Human beings have witnessed unprecedented developments since the 1760s using precision tools and manufacturing methods that have led to ever increasing precision, from millimeter to micrometer, to single nanometer, and to atomic levels. Researchers led by Prof. Fengzhou Fang from Tianjin University/University College Dublin have recently reviewed the development Atomic and Close to atomic Scale Manufacturing (ACSM) based on atomic level operation modes in subtractive, transformative, and additive manufacturing processes. Fang has formally proposed three phases of manufacturing advances: •	Manufacturing I: Craft based manufacturing by hand, as in the Stone, Bronze, and Iron Ages, in which manufacturing precision is at the millimeter scale. •	Manufacturing II: Precision controllable manufacturing using machinery where the material removal, transformation, and addition scales are reduced from millimeters to micrometers and nanometers.  •	Manufacturing III: Manufacturing objectives and processes directly focused on atoms, spanning the macro through the micro to the nanoscale where manufacturing is based on removal, transformation, and addition at the atomic scale, namely, atomic and close to atomic scale manufacturing. In this review article, the authors systematically analysed literatures in area of subtractive manufacturing including ultra precision machining, high energy beam machining, atomic layer etching, atomic force microscope nanomachining, where atomic wide line was achieved by focused electron beam sculpture based on 2D materials, such as transition metal dichalcogenides. Sub nanometer finish can be achieved with ultra precision polishing and atomic layer etching, where defects free and single atomic layer removal are still not possible. Atomic scale additive manufacturing, featured with macromolecular assembly with feedstocks, such as DNAs, proteins and peptides, represents atomic precision manufacturing of biological machines. Atomic scale transformative manufacturing, such as using Scanning Tunnelling Microscopy, Atomic Force Microscopy and Scanning Transmission Microscopy, has demonstrated capability for operation of single atoms. They also summarized the metrology technologies for ACSM and current applications. Today, the famous Moore’s law is approaching its physical limit. Computer microprocessors, such as the recently announced A12 Bionic chip and Kirlin 980, use a 7 nm manufacturing process with 6.9 billion transistors in a centimeter square chip. Such limits have been pushed to a 5 nm node and even a 3 nm node, which represents a few tens of atoms. Human beings are already stepping into the atomic era. Meanwhile, human society is facing unprecedented global challenges from depleting natural resources, pollution, climate change, clean water, and poverty.What shall we do? Such challenges are directly linked to the physical characteristics of our current technology base for producing energy and material products. According to the authors, it is the time to start changing both products and means of production via ACSM, which includes all of the steps necessary to convert raw materials, components, or parts into products designed to meet users' specifications. They believe research should focus on extensive study of fundamental mechanisms of ACSM, development of new functional devices, exploration of ACSM of extensive materials and amplifying throughput for future production.

https://iopscience.iop.org/article/10.1088/2631-7990/ab0dfc/pdf

Towards atomic and close-to-atomic scale manufacturing

Patterning materials efficiently at the smallest length scales is a longstanding challenge in nanotechnology. Electron-beam lithography (EBL) is the primary method for patterning arbitrary features, but EBL has not reliably provided sub-4 nm patterns. The few competing techniques that have achieved this resolution are orders of magnitude slower than EBL. In this work, we employed an aberration-corrected scanning transmission electron microscope for lithography to achieve unprecedented resolution. Here we show aberration-corrected EBL at the one nanometer length scale using poly(methyl methacrylate) (PMMA) and have produced both the smallest isolated feature in any conventional resist (1.7 ± 0.5 nm) and the highest density patterns in PMMA (10.7 nm pitch for negative-tone and 17.5 nm pitch for positive-tone PMMA). We also demonstrate pattern transfer from the resist to semiconductor and metallic materials at the sub-5 nm scale. These results indicate that polymer-based nanofabrication can achieve feature s...

Aberration-Corrected Electron Beam Lithography at the One Nanometer Length Scale.

Lithographic precision is as or more important than resolution. For decades, the semiconductor industry has been able to work with ±5% precision. However, for other applications such as micronanoelectromechanical systems, optical elements, and biointerface applications, higher precision is desirable. Lyding et al. [Appl. Phys. Lett. 64, 11 (1999)] have demonstrated that a scanning tunneling microscope can be used to remove hydrogen (H) atoms from a silicon (100) 2 × 1 H-passivated surface through an electron stimulated desorption process. This can be considered e-beam lithography with a thin, self-developing resist. Patterned hydrogen layers do not make a robust etch mask, but the depassivated areas are highly reactive since they are unsatisfied covalent bonds and have been used for selective deposition of metals, oxides, semiconductors, and dopants. The depassivation lithography has shown the ability to remove single H atoms, suggesting the possibility of precise atomic patterning. This patterning proces...

/pdf/atomic-precision-lithography-on-si-1z9wogdks9.pdf

Atomic precision lithography on Si

Directed microassembly and nanoassembly is performed by using appropriately-sized end-effectors coupled to macro-robotic systems. The larger end-effectors are made via microelectromechanical systems (MEMS) fabrication processes and can handle components ranging from hundreds of microns in size down to ten nanometers. Smaller end-effectors are etched tungsten probes capable of manipulating nano-scale objects. We demonstrate automated and semi-automated microscale assembly while nanoscale assembly is currently done only in semi-automated ways. Resultant assembled devices include three-dimensional MEMS assemblies and carbon nanotube structures.

Assembly technology across multiple length scales from the micro-scale to the nano-scale

http://www.scottschmucker.com/documents/Randall_MEE_2010_AuthorsPost.pdf

Atomic precision patterning on Si: An opportunity for a digitized process

We present a study addressing the effectiveness of a monolayer of hydrogen as the lithographic resist for controlled three-dimensional (3D) growth of nanostructures on the Si(100) surface. Nanoscale regions on the H-terminated Si(100) were defined by H-desorption lithography via the biased tip of a scanning tunneling microscope (STM) to create well-defined regions of surface “dangling bonds,” and the growth of 3D nanostructures within these regions was achieved using a simultaneous disilane deposition and STM H-desorption technique. We demonstrate that 3D growth is strongly confined within STM depassivated regions while unpatterned H:Si(100) regions are robust against adsorption of the precursor molecules.

J. R. Von Ehr

Papers

Atomic precision lithography on Si

Assembly technology across multiple length scales from the micro-scale to the nano-scale

Atomic precision patterning on Si: An opportunity for a digitized process

Using patterned H-resist for controlled three-dimensional growth of nanostructures

Automated Scanning Tunneling Microscope image analysis of Si (100): H 2 × 1 surfaces