Point-contact Transistors Research Articles

Fast turnaround fabrication of silicon point-contact quantum-dot transistors using combined thermal scanning probe lithography and laser writing

The fabrication of high-performance solid-state silicon quantum-devices requires high resolution patterning with minimal substrate damage. We have fabricated room temperature (RT) single-electron transistors (SETs) based on point-contact tunnel junctions using a hybrid lithography tool capable of both high resolution thermal scanning probe lithography and high throughput direct laser writing. The best focal z-position and the offset of the tip- and the laser-writing positions were determined in situ with the scanning probe. We demonstrate <100 nm precision in the registration between the high resolution and high throughput lithographies. The SET devices were fabricated on degenerately doped n-type >1020/cm3 silicon on insulator chips using a CMOS compatible geometric oxidation process. The characteristics of the three devices investigated were dominated by the presence of Si nanocrystals or phosphorous atoms embedded within the SiO2, forming quantum dots (QDs). The small size and strong localisation of electrons on the QDs facilitated SET operation even at RT. Temperature measurements showed that in the range 300 K > T > ∼100 K, the current flow was thermally activated but at <100 K, it was dominated by tunnelling.

Excited states and quantum confinement in room temperature few nanometre scale silicon single electron transistors

Single nanometre scale quantum dots (QDs) have significant potential for many ‘beyond CMOS’ nanoelectronics and quantum computation applications. The fabrication and measurement of few nanometre silicon point-contact QD single-electron transistors are reported, which both operate at room temperature (RT) and are fabricated using standard processes. By combining thin silicon-on-insulator wafers, specific device geometry, and controlled oxidation, <10 nm nanoscale point-contact channels are defined. In this limit of the point-contact approach, ultra-small, few nanometre scale QDs are formed, enabling RT measurement of the full QD characteristics, including excited states to be made. A remarkably large QD electron addition energy ∼0.8 eV, and a quantum confinement energy ∼0.3 eV, are observed, implying a QD only ∼1.6 nm in size. In measurements of 19 RT devices, the extracted QD radius lies within a narrow band, from 0.8 to 2.35 nm, emphasising the single-nanometre scale of the QDs. These results demonstrate that with careful control, ‘beyond CMOS’ RT QD transistors can be produced using current ‘conventional’ semiconductor device fabrication techniques.

History of Semiconductors

The history of semiconductors is presented beginning with the first documented observation of a semiconductor effect (Faraday), through the development of the first devices (point-contact rectifiers and transistors, early field-effect transistors) and the theory of semiconductors up to the contemporary devices (SOI and multigate devices).

Intraorganizational Alignment and Innovation Processes: Philips and Transistor Technology

The Dutch company Philips succeeded in producing transistors early on. By the early 1950s, it had acquired a strong position in the European semiconductor market. However, by the end of the 1950s, it was being surpassed by competitors. In response to the developments in solid state electronics, Philips' management adjusted the company's research, development, and production capabilities, enabling the firm to bring point-contact and layer transistors onto the market and to develop its own high-frequency transistor. When demand for industrial transistors increased, Philips was unprepared, leaving it without an entrée to this new market. The company's exclusive contracts with IBM not only failed to produce the expected results; they also limited its ability to establish ties with other computer companies and most important it illustrated Philips' choice not to produce computers. Therefore, Philips did not build knowledge and expertise in the computer field. Philips' organizational structure hampered both its innovative capacity in the field of applications and its ability to adjust transistor requirements to suit customer needs. Thus, by the early 1960s, Philips found itself in a weakened position in the increasingly competitive transistor market.

Observation of interdot coupling phenomena in nanocrystalline silicon point-contact structures

We have investigated the electrostatic and coherent couplings in 30 nm · 30 nm · 40 nm nanocrystalline silicon side gated point-contact transistors where the nanocrystalline silicon grains (10–35 nm in size) formed naturally coupled quantum dots through the thin grain boundary layers. Measurement at 4.2 K of the current as a function of the gate voltages in some thermally oxidised and high temperature annealed devices showed switching of the Coulomb oscillation peaks that was associated with electrostatic coupling between two major nanocrystals embedded in the point-contact channel. We also observed in similar measurements, using an oxidised-only device, an enhanced switching of the peaks with additional peak structures in the switching region where the grains coupled strongly. The characteristics in this region were well fitted to a sum of four Lorentzian peaks. These peaks were associated with coherent tunnelling of the electrons through the delocalised electron wavefunctions over the strongly coupled grains across the low and thin grain boundary tunnel barriers.

Inter-grain coupling effects on Coulomb oscillations in dual-gated nanocrystalline silicon point-contact transistors

Inter-grain electron-coupling effects are investigated at 4.2 K in dual-gated, point-contact, single-electron transistors fabricated in nanocrystalline silicon. The nanocrystalline silicon film is ∼40 nm thick, with grains ∼10–30 nm in size. The point-contact transistor channel is ∼30 nm×30 nm×40 nm in size, with two side-gates. Only a few grains exist within the channel and different grains contribute in varying degrees to the device conduction. By modifying the inter-grain coupling using selective oxidation of the grain boundaries, both electrostatic and wavefunction-coupling effects can be observed in the Coulomb oscillations vs. the two gate voltages.

Switching of single-electron oscillations in dual-gated nanocrystalline silicon point-contact transistors

Switching of single-electron transport is observed in point-contact transistors fabricated in nanocrystalline silicon thin films, where the grain size is /spl sim/10 to 40 nm. The effects may be associated with electrostatic coupling between the grains. At 4.2 K, single-electron oscillations in the device current are switched as a function of the voltages on two separate gates. This is investigated further using single-electron Monte Carlo simulation of a model with two charging grains in parallel and intergrain capacitive coupling. A change in the electron number of a grain occurs due to charging of the other grain by a single electron, causing bistable regions in charge stability versus gate voltage. These effects depend not only on the coupling capacitance but also on the cross capacitances between the grains and the two gates.

Single-Electron Charging Phenomena in Nano/Polycrystalline Silicon Point Contact Transistors

Single-Electron Charging Phenomena in Nano/Polycrystalline Silicon Point Contact Transistors

Single-electron charging in nanocrystalline silicon point-contacts

Room-temperature single-electron effects are observed in 20 nm × 20 nm point-contact transistors fabricated in nanocrystalline silicon thin films. The films are deposited using low-temperature plasma enhanced chemical vapour deposition and contain grains typically 4-8 nm in size. Low-temperature oxidation and high-temperature annealing is used to oxidise selectively the grain boundaries. Single-electron effects occur in crystalline silicon grains isolated by tunnel barriers at the grain boundaries. The thermal processing improves the grain-boundary tunnel barrier and increases the maximum temperature for single-electron effects. Similar effects are also observed in devices fabricated in low-pressure chemical vapour deposited polysilicon films.

Characterization of Tunnel Barriers in Polycrystalline Silicon Point-Contact Single-Electron Transistors

Potential barrier properties of grain boundaries in polycrystalline silicon have been studied using nanometer-scale point-contact transistors. The devices, with channel length and width ranging from 30 nm to 50 nm, were fabricated in a 50-nm-thick film. We found that grain boundaries oxidized at 1000°C acted as tunneling barriers, resulting in the appearance of single-electron charging effects. However, potential barrier heights estimated for oxidized grain boundaries are still low, less than 90 meV, and barrier thickness is as large as ∼4 nm. The grain boundary oxides appear to be silicon sub-oxides which are formed by oxygen diffusion into grain boundaries.

Electronic transport at semiconductor surfaces––from point-contact transistor to micro-four-point probes

The electrical properties of semiconductor surfaces have played a decisive role in one of the most important discoveries of the last century, transistors. In the 1940s, the concept of surface states––new electron energy levels characteristic of the surface atoms––was instrumental in the fabrication of the first point-contact transistors, and led to the successful fabrication of field-effect transistors. However, to this day, one property of semiconductor surface states remains poorly understood, both theoretically and experimentally. That is the conduction of electrons or holes directly through the surface states. Since these states are restricted to a region only a few atom layers thick at a crystal surface, any signal from them might be swamped by conduction through the underlying bulk semiconductor crystal, as well as greatly perturbed by steps and other defects at the surface. Yet recent results show that this type of conduction is measurable using new types of experimental probes, such as the multi-tip scanning tunnelling microscope and the micro-four-point probe. The resulting electronic transport properties are intriguing, and suggest that semiconductor surfaces should be considered in their own right as a new class of electronic nanomaterials because the surface states have their own characters different from the underlying bulk states. As microelectronic devices shrink even further, and surface-to-volume ratios increase, surfaces will play an increasingly important role. These new nanomaterials could be crucial in the design of electronic devices in the coming decades, and also could become a platform for studying the physics of a new family of low-dimensional electron systems on nanometre scales.

Hands Free in the Office

Accessible online at: http://BioMedNet.com/karger I first used a computer about 35 years ago. I forget the exact date but I do remember the problem we were trying to solve. It was to deconvolute a complex spectrogram from the analysis of a mixture of three compounds. Today this complex mathematical procedure requires only the push of a button. It is a ‘feature’ of many modern machines. However, in those distant days before digital watches the calculation was a major undertaking. The computer programme had to be written, punched onto paper tape and translated into machine code in the airconditioned room filled with large grey boxes of electronics and a control console that was the computer. The machine then output the machine code on another reel of paper tape. Next, the data was punched onto paper tape, translated and more paper tape generated. Finally the programme could be run, the data input and the result calculated. The technology has come a long way since then, a very long way. We now live in a world full of technology, surrounded by complex electronic machinery controlled by yet more technology. Even that machine-made-God so beloved by science fiction and comic book writers, the super-computer, has been around for a number of years although we have not yet arrived at the scenario of a supermachine that rules the world. Not yet – perhaps the Internet will evolve. Anyway, why this harping on about computers and the march of technology? Well, it is because I can remember point contact transistors, the first chips and hard-wired memory and how I watched in wonder as they evolved into the Pentium microprocessor and continue to evolve and I still have a sense of wonder. I also remember the frustration of typing when one was not a typist, the despair as fingers with a will of their own hit the wrong keys and the matchless prose was peppered with errors and had to be re-typed. To have access to, or better to own, a machine which allowed one to correct and to overtype and to re-correct text was magical. The word-processor is a wonderful invention, much, much more than just a clever typewriter. QWERTYUIOP was old when I was born, but I have welcomed the mouse and admired the touch screen, both partial substitutes for 10 fingers tapping out a pattern on a keyboard, or in my case 2 fingers stabbing at a field of keys. Technology marches on and it seems that finger stabbing days are coming to an end. When we want to communicate with people who are close by, we generally speak to them. However, this is a very complicated thing to do. The vocal system is so incredibly complex when compared to just 10 fingers picking out 26 letters and 10 numbers to form the same message. It never seemed possible that what has taken human beings more than 100,000 years to develop could be built as a machine over two or three decades. We have evolved a voice and language and now the computer can understand it. Engineers have been trying for a long time to develop a good voice recognition system. The first experiments and trials were many years ago when with perseverance and luck the computer would learn to recognise a spoken word. With considerable application a well-trained computer could probably recognise 100 words. Quite quickly it seems the technology has moved on and now anyone with a computer, albeit a modern computer but still just a PC, can have quite cheaply software which enables you to control the computer, hands free, just by speaking to it at normal conversational speed.

Physical characterization of electron trapping in Unibond(R) oxides

In this work, we study the trapping properties of Unibond(R) oxides. We measure its radiative response under different irradiation conditions using both point-contact and MOS transistors. The results obtained show both hole and electron trapping, as previously observed in SIMOX. But in the Unibond(R) case, there is a positive shift of the threshold voltage at very high doses. Using a simple model, we explain this shift by considering a second type of electron traps.

Transistor Electronics: Imperfections, Unipolar And Analog Transistors

The electronic mechanisms that are of chief interest in transistor electronics are discussed from the point of view of solid-state physics. The important concepts of holes, electrons, donors, acceptors, and deathnium (recomibination center for holes and electrons) are treated from a unified viewpoint as imperfections in a nearly perfect crystal. The behavior of an excess electron as a negative particle moving with random thermal motion and drifting in an electric field is described in detail. A hole is similar to an electron in all regards save sign of charge. Some fundamental experiments have been performed with transistor techniques and exhibit clearly the behavior of holes and electrons. The interactions of holes, electrons, donors, acceptors, and deathnium give rise to the properties of p-n junctions, p-n junction transistors, and Zener diodes. Point-contact transistors are not understood as well from a fundamental viewpoint. A new class of unipolar transistors is discussed. Of these, the analog transistor is described in terms of analogy to a vacuum tube.

High-temperature point-contact transistors and Schottky diodes formed on synthetic boron-doped diamond

Point-contact transistors and Schottky diodes have been formed on synthetic boron-doped diamond. This is the first report of diamond transistors that have power gain. Further, the transistors exhibited power gain at 510°C and the Schottky diodes were operational at 700°C.

Early Transistor Computers in Japan

The paper describes the history of the early development of transistor computers in Japan. Because the paper pertains mostly to the Electronics Division of the Electrotechnical Laboratory, the author begins with the establishment of this division. He then explores the development of the ETL Mark III, which used point-contact transistors, and the ETL Mark IV, which was followed by various commercial products. ETL Mark IV technology was also employed for "Yamato, " a special-purpose machine that was developed in 1959 for the first trial of English-Japanese machine translation.

Equivalent base resistance of point-contact transistors

A theoretical expression for the equivalent base resistanceR b of point-contact transistors is derived by consideration of a three-dimensional electric field problem. The analysis shows that the equivalent base resistance depends on the location of the emitter, resistivity of the semiconductor and the dimensions of the configuration.

Operating experience with a transistor digital computer

A small digital computer using transistors as the only active circuit elements has been operating for a year. The paper describes the performance of this computer and, in particular, the failure rate of point-contact transistors. Earlier information on this computer is supplemented by details of circuit developments.

Developments in Transistor Electronics†

ABSTRACT The design theory of point-contact and junction transistors is reviewed in this paper. Selected examples illustrate the small-signal and large-signal properties of junction transistors. These phenomena are related to the theory of p— n junctions. Also, it is indicated how circuit engineers benefit from a certain know-ledge of transistor theory.

IRE Standards on Solid-State Devices: Methods of Testing Point-Contact Transistors for Large-Signal Applications, 1958

IRE Standards on Solid-State Devices: Methods of Testing Point-Contact Transistors for Large-Signal Applications, 1958