Tag Archives: Transistor

Coulomb Transistor — A New Concept Where Metal Nanoparticles Are Used In Place Of Semiconductor

A research group at the University of Hamburg has created a unique coulomb transistor that operates on the principle of the voltage control of the electron band gap in metallic quantum-dot nanoparticles. This Single-electron transistor represents an approach to develop less power-consuming microelectronic devices. It will be possible if industry-compatible fabrication and room temperature operation are achieved.

The concept is based on building stripes of small, colloidal, metal nanoparticles on a back-gate device architecture. Being very tiny, the metallic nanoparticles exhibit semiconductor properties that can be controlled by voltage. The body of this transistor can be operated as a second gate. It results in well-defined and controllable transistor characteristics.

Design of coulomb transistor
Design of Coulomb transistor

This newly invented Coulomb transistor has three main advantages. The advantages are: on/off ratios above 90%, very reliable and sinusoidal Coulomb oscillations, and room temperature operation. The concept allows for tuning of the device properties such as Coulomb energy gap and threshold voltage, as well as the period, position, and strength of the oscillations.

Though the single-electron transistor (SET) is quite similar to a common field-effect transistor (FET), it does not rely on the semiconductor band gap but instead on the Coulomb energy gap. Transfer characteristics of the SET show periodic on and off states known as Coulomb oscillations. Researchers hope that might render new applications possible in the future.

When a bias voltage is applied to the nanoparticle channel, it becomes clear that conduction in this system is not purely metallic but is controlled by tunnel barriers between individual particles. The transport of charged particles is hindered due to very high potential barrier which depends on the charging energy. Tuning the voltage of an additional gate results in a field effect that continuously shifts the energy levels of the particles and allows for tunneling to occur. This additional gate electrode is separated from the channel by a dielectric layer.

Output characteristics of coulomb transistor
Output characteristics of Coulomb transistor

The single-electron transistors require further research and more development, but the work shows that there are alternatives to traditional transistor concepts that can be used in the future in various fields of application. Christian Klinke, the lead researcher, said in a statement,

The devices developed in our group can not only be used as transistors, but they are also very interesting as chemical sensors because the interstices between the nanoparticles, which act as so-called tunnel barriers, react highly sensitive to chemical deposits.

Diamond-Based MOSFETs Are Now Real

A research group at Japan’s National Institute for Materials Science (NIMS) has developed logic circuits equipped with diamond-based metal-oxide-semiconductor field-effect-transistors (MOSFETs) at two different operation modes – a first step toward the development of diamond integrated circuits operational under extreme environments.

Is Diamond Suitable for this?

In fact, diamond has high carrier mobility, a high breakdown electric field and high thermal conductivity. Therefore, it is a promising material to use in the development of current switches and integrated circuits. Specifically to operate stably at high-temperature, high-frequency, and high-power. However, it had been difficult to enable diamond-based MOSFETs to control the polarity of the threshold voltage. In addition, fabricating MOSFETs of two different modes on the same substrate was a challenge. The modes are:  a depletion mode (D mode) and an enhancement mode (E mode).

Thus, the research group has successfully developed a logic circuit equipped with modes. Thanks to threshold control technique that allowed them create hydrogenated diamond NOT and NOR logic circuits composed of D-mode and E-mode MOSFETs.

Micrograph of a fabricated logic circuit equipped with diamond-based transistors

This study was published in the online version of IEEE Electron Device Letters and it is available at the IEEE Electron Digital Library website. Also, check the official announcement for more details.

A 5nm GAAFET Chip By IBM, Samsung & GlobalFoundries

In less than two years since making a 7nm test node chip with 20 billion transistors, scientists have paved the way for 30 billion switches on a fingernail-sized chip. IBM with its Research Alliance partners, GlobalFoundries and Samsung, have unveiled their industry-first process that will enable production of 5nm chips.

The new 5nm technology is one of the first ICs based on GAAFET (Gate-All-Around) topology transistors and also probably the first serious application of EUV (Extreme UltraViolet) lithography.

5 nm GAAFET IC from IBM, Samsung & GlobalFoundries
5 nm GAAFET IC from IBM, Samsung & GlobalFoundries

Gate-all-around FETs are similar in concept to FinFETs except that the gate material surrounds the channel region on all sides. Depending on design, gate-all-around FETs can have two or four effective gates. Successfully, Gate-all-around FETs have been characterized both theoretically and experimentally. Also, they have been successfully etched onto InGaAs nanowires, which have a higher electron mobility than silicon.

IBM claims that it can fit in up to 30 Billion transistors on the chip using GAAFET on a 50 mm² chip. It’s a big move in the semiconductor world, as designs become increasingly complicated to apply. While comparing 5nm GAAFET to 10nm commercial chips, it will achieve a 40% performance boost and a 75% power consumption reduction, at similar performance levels. These are some big claims, so expect some big changes just around the corner.

“For business and society to meet the demands of cognitive and cloud computing in the coming years, advancement in semiconductor technology is essential,” said Arvind Krishna, senior vice president, Hybrid Cloud, and director, IBM Research. “That’s why IBM aggressively pursues new and different architectures and materials that push the limits of this industry, and brings them to market in technologies like mainframes and our cognitive systems.”

For more information you can visit the official announcement.

PNP Transistor – How Does It Work?

The PNP transistor is a mystery to many. But it doesn’t have to be. If you want to design circuits with transistors, it’s really worth knowing about this type of transistor. by Oyvind @ build-electronic-circuits.com

PNP Transistor – How Does It Work? – [Link]

Ultralow Power Transistors Function for Years Without Batteries

Researchers at Cambridge University have just achieved a spectacular breakthrough in electronics design. They have developed new ultralow power transistors that could function for months or even years without a battery. These transistors look for energy from the environment around, thus reducing the amount of power used.

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Dr Sungsik Lee, one of the researchers at the Department of Engineering says, “if we were to draw energy from a typical AA battery based on this design, it would last for a billion years.” The new design could be produced in low temperatures and they are versatile enough to be printed on materials like glass, paper, and plastic.

Basically, transistors are semiconductor devices that function like a faucet. Turn a transistor on and the electricity flows,  turn it off and the flow stops. When a transistor is off however, some electric current could still flow through, just like a leaky faucet. This current, which is called a near-off-state, was exploited by the engineers to power the new transistors.

power-consumption

schematicThe researchers developed a thin-film transistor (TFT) from In-Ga-Zn-O (indium-gallium-zinc-oxide) thin films. To make the material less conductive, the films were fabricated to avoid oxygen vacancies. Eventually, they achieved a new design that operates in near the OFF state at low supply voltages (<1 volt) and ultralow power (<1 nanowatt).

The transistor’s design also utilizes a ‘non-desirable’ characteristic, namely the ‘Schottky barrier’ to create smaller transistors. Transistors today cannot be manufactured into smaller sizes since the smaller a transistor gets, the more its electrodes influence each other, causing a non-functioning transistor.The use of the Schottky barrier in the new design creates seal between the electrodes that make them work independently from each other.

“We’re challenging conventional perception of how a transistor should be,” said Professor Arokia Nathan of Cambridge’s Department of Engineering, the paper’s co-author. “We’ve found that these Schottky barriers, which most engineers try to avoid, actually have the ideal characteristics for the type of ultralow power applications we’re looking at, such as wearable or implantable electronics for health monitoring.”

According to Arokia Nathan of Cambridge’s Department of Engineering, the second author of the paper, this new design can see use in various sensor interfaces and wearable devices that require only a low amount of power to run. Professor Gehan Amaratunga, Head of the Electronics, Power and Energy Conversion Group at Cambridge’s Engineering Department sees its use in more autonomous electronics that can harness energy from their environments similar to a bacteria.

As electronic devices become more compact and powerful, conventional methods for manufacturing electrical components simply won’t do. This unconventional way will not only consume minimum power but it also will open up new avenues for system design for the Internet of Things and ultralow power applications.

This research was introduced as a research paper in Science magazine on October 2016. More details are available here  “Subthreshold Schottky-barrier thin-film transistors with ultralow power and high intrinsic gain”.

The Tiniest 1nm Gate Transistor

A research team led by faculty scientist Ali Javey at Berkeley Lab have debuted the smallest transistor ever reported. A gate structure of just 1 nm long can bring Moore’s law back again after the demonstration of the recent Silicon (Si) transistor with 5 nm gate. It was predicted that transistors will fail below 5 nm gate because of some short channel effects that would change the transistor characteristics, but the new finding is proving that wrong.

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Model showing the transistor structure


Because of current leakage that would happen in less than 5-nm Si transistors, the  exploration of new channel materials that have more ideal properties than Si should begin. The researchers used carbon nanotubes and molybdenum disulfide (MoS2), an engine lubricant commonly sold in auto parts shops. MoS2 is part of a family of materials with immense potential for applications in LEDs, lasers, nanoscale transistors, solar cells, and more. Fortunately, MoS2 electronics properties as thin layers will limit leakage that happen in Si alternatives.

While the researchers started using MoS2 as the semiconductor material, they recognized the hardship of constructing the gate using it.Thus, they turned to carbon nanotubes, hollow cylindrical tubes with diameters as small as 1 nanometer. This structure made it easier to control the flow of electrons effectively.

mos2
Optical image of a representative device shows the MoS2 flake, gate (G)

This project is just a proof of concept and researchers have not yet found a way to mass-produce it or integrate it in chips. They could break the myth of the Si transistor 5-nm gate limit and they paved the way for future researchers to demonstrate a new device architecture.

With such a small scale it will be an unexpected future of tiny devices that use lots of transistors, since all the technology we use nowadays are made of transistors with minimum 7nm geometry.

The work at Berkeley Lab was primarily funded by the Department of Energy’s Basic Energy Sciences program.

This research was introduced as a research paper in Science magazine on October 2016. More details are available here  “MoS2 transistors with 1-nanometer gate lengths“.

Use a transistor as a heating element

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REC Johnson, B Lora Narayana, and Devender Sundi share their design idea on how to use a transistor as a heating element.

It is common to use transistors for driving resistive heating elements. However, you can use the heat that a power transistor dissipates to advantage in several situations, eliminating the need for a separate heating element because most transistors can safely operate at temperatures as high as 100°C. A typical example is in a biological laboratory, in which the need for maintaining the temperature of samples in microliter-sized cuvettes is a common requirement. The space/geometry constraint and the less-than-100°C upper-temperature limit are the basic factors of the idea.

Use a transistor as a heating element – [Link]

Simple two-transistor circuit lights LEDs

led-drive-circuit

Barry Tigner @ edn.com has a design idea on how to power a LED from a 1.5V battery using two easily available transistors.

A previous Design Idea describes a circuit that uses an astable multivibrator to drive an LED (Reference 1). The circuit in Figure 1 uses a simpler alternative approach. The circuit uses a 2N3904 NPN transistor and a 2N3906 PNP transistor, which operate as a high-gain amplifier.

Simple two-transistor circuit lights LEDs – [Link]

What Will Happen to Moore’s Law in 2021?

Moore’s law states that the number of transistors doubles every two years. Rachel Courtland from IEEE Spectrum explained the sharp turn of Moore’s law in 2021.

Moore2021Chip manufactures will switch to another way of boosting the density in the chip by having multilayer chips using vertical geometry, and we’ve already seen the 3D concept in silicon chips like 3D NAND Flash. According to 2015 roadmap released by International Technology Roadmap for Semiconductors (ITRS), by 2021, shrinking the dimensions of transistors in microprocessors will not be desired economically by chip makers, although the report of 2014 predicted that the physical dimensions would continue to shrink until at least 2028.

According to the article, the spirit of Moore’s Law could still there, where some changes in the technologies will still lead to pack more transistors in a given area.

Rachel also mentioned  that first international Rebooting Computing conference will be held in October this year 2016. It’s “Other ITRS participants are expected to continue on with a new roadmapping effort under a new name” Rachel said.

[Article on IEEE Spectrum]

Berkeley Lab makes graphene-MoS2 transistor

lawberkgraphmos525

U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has developed a way to assemble transistors based on the 2D materials graphene and molybdenum disulfide. By Peter Clarke @ edn-europe.com

The method etches narrow channels in conducting graphene laid down on a silicon-dioxide substrate. These channels are then filled with a transition-metal dichalcogenide, or TMDC, or more specifically MoS2. Both of these materials have a 2D structure that is just one atomic layer thick. The synthesis method was able to cover an area a few centimeters long by a few a millimeters wide opening up the possibility of commercial-scale production in a wafer fab on a silicon wafer.