Tag Archives: semiconductor

Understanding Flash Memory And How It Works

Flash memory is one of the most widely used types of non-volatile memory. NAND Flash is designed for modern file storage which replaced old disk drives. This article provides a brief understanding of how NAND Flash technology works.

The basic storage component used in Flash memory is a modified transistor. In a standard transistor, the flow of current through a channel between two contacts is turned on by a voltage applied to the gate. The channels are separated by an insulating layer of Oxide. In a Flash storage cell, there is an extra electrically isolated gate called “floating gate”. It is added to the control gate and the channel of the modified transistor.

Different Flash Storages
Different Flash Memory Devices

High voltage is applied to the control gate of The Flash cell to program it. This pushes electrons to pass through the oxide layer to the floating gate (a process known as tunneling). The presence of these trapped electrons on the floating gate changes the required voltage to turn on the transistor. Thus, a transistor with no charge on the floating gate can easily turn on at a certain voltage, representing a 1, while a programmed cell will not turn on, representing a 0.

This kind of memory is non-volatile because the floating gate is surrounded by dielectric layers, it traps the electric charge even when the power is removed. Erasing a cell reverses this process by introducing a large negative voltage to the control gate to force the electrons to tunnel out of the floating gate.

NANAD Flash storage internal
NAND Flash Memory storage internal

A number of cells, typically 32 to 128, are connected in a string. Strings are organized in blocks. To program cells in a block, the data is put on the bit lines and a high voltage is applied. Because programming can only change a cell from a 1 to a 0, any cells where the new data is a 1, will be left in their current state. Therefore, all the cells must be erased before writing. This process ensures that any cells that will not be programmed already contain a 1.

As explained above, each cell can store a single binary value, 0 or 1. It is also possible to inject varying amounts of charge onto the floating gate so that the cell can express multiple values. A multi-level cell (MLC) can store four different levels to represent two bits. However, the performance is reduced because of the complexity of accurate voltage controls. For the same reason, MLC Flash memory is more inclined to errors.

Although flash memory has a limited number of write-erase cycles, the high voltages cause a small amount of damage to the cells which makes them harder to read-write over time. The main drawback of using a flash memory is that it has a lifetime of about 100,000 cycles or fewer for MLC Flash.

Physicists Of University of Rochester Have Created Polariton – A Particle With Negative Mass

A group of researchers led by Nick Vamivakas from the University of Rochester has successfully produced particles which have negative mass in an atomically thin semiconductor material. According to the researchers, they have created a device that can generate LASER light using a significantly small amount of energy. All made possible with the help of this so-called negative mass particles. Quantum physicist Nick Vamivakas from Rochester’s Institute of Optics says,

It also turns out the device we’ve created presents a way to generate laser light with an incrementally small amount of power. Interesting and exciting from a physics perspective,

Polariton – A new particle that has negative mass

Mass is often observed as a resistance or response to a force. It’s harder to push and to stop a bowling ball than a marble because of the inertia associated with the mass of the object. All objects that are made of matter must have the property of ‘mass’. Even elementary particles without rest mass have something called relativistic mass. They react to an externally applied force in the way you expect them to. Particles with ‘negative mass’ however exhibit the opposite reaction to an applied force. They tend to move toward the applied force direction than to move away from it.

“That’s kind of a mind-bending thing to think about because if you try to push or pull it, it will go in the opposite direction from what your intuition would tell you,” says Vamivakas.

The device they created to make negative mass consists of two mirrors. It is used to make an optical microcavity to capture light at different colors of the spectrum depending on the mirror spacing. An atomically thin Molybdenum diselenide semiconductor is then implanted into the microcavity. This interacts with the captured light. The small particles called excitons from the semiconductor combine with photons of the trapped light to form polaritons. This process of an exciton giving up its identity to a photon to produce a polariton results in an object with negative mass associated with it. Simply means when you try to push or pull it, it goes off in the opposite direction to the way you would assume.

The most probable practical applications according to the researchers would be:

  •  The physics of negative mass: It will enrich the understanding of the reaction behavior of polaritons on electric fields and external forces.
  •  As a laser fabrication substrate: Due to polaritons, lasers would function more efficiently than the conventional ones. They will require much lower power input.

Further information is available in the journal Nature Physics, with the title Anomalous dispersion of microcavity trion-polaritons.

World’s Smallest MEMS Micro-Loudspeaker Saves 80 Percent More Energy

STMicroelectronics along with the audio company USound has created the first MEMS (Micro ElectroMechnical Systems) micro-loudspeaker based on semiconductors. It’s the smallest loudspeaker in the world, but it can produce a powerful noise. MEMS makes it possible. The speakers are being presented at CES 2018 in Las Vegas.

MEMS loudspeaker with extremely small dimensions along with low power consumption and good sound quality.
MEMS loudspeaker with extremely small dimensions along with low power consumption and good sound quality.

In the audio world, the electromechanical capabilities of MEMS have only been used to build tiny microphones. Speakers, on the other hand, still rely on traditional dynamic design principles. It has taken almost 150 years for semiconductor technology to replace Werner von Siemens’ superior loudspeaker principle in 1877 with something newer. The Coil-magnet combinations are still being used in smartphones, wearables, and headphones to produce sound.

We can understand the working principle of MEMS speaker very briefly here. At first, thin piezoelectric layers are applied to a semiconductor(Silicon). An electric signal is sent to the piezoelectric layer allowing the diaphragm connected to it vibrate. Eventually, the mechanical principle resembles that of a normal Coil-magnet loudspeaker. The sound is created by the vibration in the diaphragm. However, the magnet and coil are replaced by a piezo element. By applying this new technique, USound’s MEMS version appears to offer significant advantages when it comes to distortion and THD or Total Harmonic Distortion.

The MEMS loudspeaker developed by USound has dimensions of just 5 x 7 x 2 mm and has a frequency range of 2 to 15 kHz. It takes up half the space of its predecessors and needs only 20 percent of the energy that they do. The above figures are convincing enough for the speaker to be a perfect fit for mobile applications such as wearables and smartphones.

According to the manufacturer, these tiny speakers are the thinnest in the world. It has less than half the weight of a conventional Coil-magnet speaker. Most suitable applications include in many portable devices such as headphones, over-the-ear earphones, and more. With the help of this new speakers, augmented reality headsets or virtual reality systems can be more compact and comfortable. Innovative features also enable 3D sound production with striking accuracy. Its high efficiency reduces energy consumption and can easily be operated with much smaller and lightweight batteries. Higher efficiency results in less heat generated making systems operate cooler than ever before.

Researchers Demonstrate New More Efficient FET By Implementing Negative Capacitance

A group of Researchers from Purdue University in Lafayette, Indiana demonstrated the effect called negative capacitance by making a new type of more energy efficient transistor. This new kind of Field Effect Transistor (FET) proves a theory introduced in 2008 by Supriyo Datta, the Thomas Duncan Distinguished Professor of Electrical and Computer Engineering, and Sayeef Salahuddin, who is a professor of Electrical Engineering and Computer Sciences at the University of California, Berkeley.

A new type of transistor (a) harnesses a property called negative capacitance.
A new type of field effect transistor harnesses a property called negative capacitance.

The researchers from Purdue University made a much thinner layer using the semiconductor Molybdenum disulfide. It creates a channel adjacent to an important part of transistors called the gate. By using a “ferroelectric material” called hafnium zirconium oxide, they created a negative capacitor which is a key component in the newly designed gate.

Capacitance is the property of any dielectric or conductor to store electrical charge. It is ordinarily a positive quantity. With the help of ferroelectric materials, the new FET gate structure allows a negative capacitance. Due to this the energy needed to switch the FET is considerably reduced. This new design just substitutes hafnium oxide with hafnium zirconium oxide. Hafnium oxide is a conventional material to use in modern FETs as a dielectric material to isolate the gate. This work is led by Peide Ye, Richard J. and Mary Jo Schwartz of Purdue University.  Ye said,

The overarching goal is to make more efficient transistors that consume less power, especially for power-constrained applications such as mobile phones, distributed sensors, and emerging components for the internet of things

Transistors act like a tiny electronic switch. They can turn on and off very fast, allowing computers to process information in binary code. A proper switching off state is very important to ensure that no electricity “leaks” through. This switching normally needs a minimum of 60 millivolts for every tenfold increase in current. This requirement called the thermionic limit. However, transistors using negative capacitance can break this fundamental limit, because they can switch at far lower voltages resulting in smaller power consumption.

New findings from the research group have advanced the conventional transistor technology to a much efficient and faster level. Only time will justify if the new ‘negative capacitance‘ FETs can revolutionize the modern electronics.

New Ultrathin Semiconductors Can Make More Efficient and Ten Times Smaller Transistors Than Silicon

The researchers at Stanford University have discovered two ultrathin semiconductors – hafnium diselenide and zirconium diselenide. They share or even exceed some of the very important characteristics of silicon. Silicon has a great property of forming “rust” or silicon dioxide (SiO2) by reacting with oxygen. As the SiO2 acts as an insulator, chip manufacturers implement this property to isolate their circuits on a die. The most interesting fact about these newly discovered semiconductors is, they also form “rust” just like silicon.

enlarged cross-section of an experimental chip made of ultrathin semiconductors
An enlarged cross-section of an experimental chip made of ultrathin semiconductors

The new materials can also be contracted to functional circuits just three atoms thick and they require much less energy than silicon circuits. Hafnium diselenide and zirconium diselenide “rust” even better than silicon and form so-called high-K insulator. The researchers hope to use these materials to design thinner and more energy-efficient chips for satisfying the needs of future devices.

Apart from having the ability to “rust”, the newly discovered ultrathin semiconductors also have the perfect range of energy band gap – a secret feature of silicon. The band gap is the energy needed to switch transistors on and it is a critical factor in computing. Too low band gap causes the circuits to leak and make unreliable. Too high and the chip takes excessive energy to operate and becomes inefficient. Surprisingly, Hafnium diselenide and zirconium diselenide are in the same optimal range of band gap as silicon.

All this and the diselenides can also be used to make circuits which are just three atoms thick, or about two-thirds of a nanometer, something silicon can never do. Eric Pop, an associate professor of electrical engineering, who co-authored with post-doctoral scholar Michal Mleczko in a study paper, said,

Engineers have been unable to make silicon transistors thinner than about five nanometers, before the material properties begin to change in undesirable ways.

If these semiconductors can be integrated with silicon, much longer battery life and much more complex functionality can be achieved in consumer electronics. The combination of thinner circuits and desirable high-K insulation means that these ultrathin semiconductors could be made into transistors 10 times tinier than anything possible with silicon today. As Eric Pop said,

There’s more research to do, but a new path to thinner, smaller circuits – and more energy-efficient electronics – is within reach.

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.

SUNY Polytechnic Creates 3-in-1 Device That Can Be A Diode, A MOSFET And A BJT

In a recently published study, a team of researchers at SUNY Polytechnic Institute in Albany, New York, has suggested that combining multiple functions in a single semiconductor device can significantly improve device’s functionality and efficiency.

Nowadays, the semiconductor industry is striving to scale down the device dimensions in order to fit more transistors onto a computer chip and thus improve the speed and efficiency of the devices. According to Moore’s law, the number of transistors on a computer chip cannot exponentially increase forever. For this reason, scientists are trying to find other ways to improve semiconductor technologies.

To demonstrate the new technology which can be an alternative to Moore’s law, the researchers of SUNY Polytechnic designed and fabricated a reconfigurable device that can be a p-n diode (which functions as a rectifier), a MOSFET (for switching), and a bipolar junction transistor (or BJT, for current amplification). Though these three devices can be fabricated individually in modern semiconductor fabrication plants, it often becomes very complex if they are to be combined.

reconfigurable 3-in-1 semiconductor device
the reconfigurable 3-in-1 semiconductor device

Ji Ung Lee at the SUNY Polytechnic Institute said,

We are able to demonstrate the three most important semiconductor devices (p-n diode, MOSFET, and BJT) using a single reconfigurable device. We can form a single device that can perform the functions of all three devices.

The multitasking device is made of 2-D tungsten diselenide (WSe2), a new transition metal dichalcogenide semiconductor. This class of materials is special as the bandgap is tunable by varying the thickness of the material. It is a direct bandgap while in single layer form.

Another challenge was to find a suitable doping technique as WSe2 lacks one being a new material. So, to integrate multiple functions into a single device, the researchers developed a completely new doping method. By doping, the researchers could obtain properties such as ambipolar conduction, which is the ability to conduct both electrons and holes under different conditions. Lee said,

Instead of using traditional semiconductor fabrication techniques that can only form fixed devices, we use gates to dope.

These gates can control which carriers (electrons or holes) should flow through the semiconductor. In this way, the ambipolar conduction is achieved. The ability to dynamically change the carriers allows the reconfigurable device to perform multiple functions. Another advantage of using gates in doping is, it saves overall area and enable more efficient computing. As consequence, the reconfigurable device can potentially implement certain logic functions more compactly and efficiently.

In future, researchers plan to investigate the applications of this new technology and want to enhance its efficiency further. As Lee said,

We hope to build complex computer circuits with fewer device elements than those using the current semiconductor fabrication process. This will demonstrate the scalability of our device for the post-CMOS era.

ReRAM, Process Data Where They Are Stored

Because data storage and processor are separated from each other, moving data between the storage and the computation unit became a main factor in computing.
Many techniques were developed to speed up this process, such as pipelining, caching, and look-ahead execution, but “ReRAM” appears as a new technique to solve the root of the problem by merging memory and processor together.

Resistive RAM, which known as RRAM or RERAM, is the new generation of memories. Its cells are simpler than classic transistor-based memory cells, they are non-volatile, switch fast and can run from low voltages. Researchers now have managed to make RERAM cells store more than just a ‘0’ or a ‘1’, enabling in-place computations.

The first small memory devices based on this technology is the MB85AS4MT, that was developed by Fujitsu Semiconductor with Panasonic Semiconductor Solutions. MB85AS4MT is a 4 Mbit ReRAM chip that operates with a supply voltage in the range from 1.65 to 3.6 V and has an SPI interface. One of the stand-out features of this technology is its low operating current, just 0.2 mA, at a maximum read speed of 5 MHz.

Using so-called RERAM crossbar arrays, researchers have demonstrated the in-memory execution of binary matrix computations frequently encountered in high-performance computing, algebraic cryptanalysis, combinatorics and finite geometry data, and in general large scale data analysis. Although we are only at the beginning of this technology, the results are already promising.

More mathematical details can be found in this paper.

Source: elektor.

The Next-Generation Semiconductor for Power Electronics

Researchers have demonstrated the high-performance potential of an experimental transistor made of a semiconductor called beta gallium oxide, which could bring new ultra-efficient switches for applications such as the power grid, military ships and aircraft.

The semiconductor is promising for next-generation “power electronics,” or devices needed to control the flow of electrical energy in circuits. Such a technology could help to reduce global energy use and greenhouse gas emissions by replacing less efficient and bulky power electronics switches now in use.

The schematic at left shows the design for an experimental transistor made of a semiconductor called beta gallium oxide, which could bring new ultra-efficient switches for applications such as the power grid, military ships and aircraft. At right is an atomic force microscope image of the semiconductor. (Purdue University image/Peide Ye)

 

The schematic at left shows the design for an experimental transistor made of a semiconductor called beta gallium oxide, which could bring new ultra-efficient switches for applications such as the power grid, military ships and aircraft. At right is an atomic force microscope image of the semiconductor. (Purdue University image/Peide Ye)The transistor, called a gallium oxide on insulator field effect transistor, or GOOI, is especially promising because it possesses an “ultra-wide bandgap,” a trait needed for switches in high-voltage applications.

Compared to other semiconductors thought to be promising for the transistors, devices made from beta gallium oxide have a higher “breakdown voltage,” or the voltage at which the device fails, said Peide Ye, Purdue University’s Richard J. and Mary Jo Schwartz Professor of Electrical and Computer Engineering.

Findings are detailed in a research paper published this month in IEEE Electron Device Letters. Graduate student Hong Zhou performed much of the research.

The team also developed a new low-cost method using adhesive tape to peel off layers of the semiconductor from a single crystal, representing a far less expensive alternative to a laboratory technique called epitaxy. The market price for a 1-centimeter-by-1.5-centimeter piece of beta gallium oxide produced using epitaxy is about $6,000. In comparison, the “Scotch-tape” approach costs pennies and it can be used to cut films of the beta gallium oxide material into belts or “nano-membranes,” which can then be transferred to a conventional silicon disc and manufactured into devices, Ye said.

The technique was found to yield extremely smooth films, having a surface roughness of 0.3 nano-meters, which is another factor that bodes well for its use in electronic devices, said Ye, who is affiliated with the NEPTUNE Center for Power and Energy Research, funded by the U.S. Office of Naval Research and based at Purdue’s Discovery Park. Related research was supported by the center.

The Purdue team achieved electrical currents 10 to 100 times greater than other research groups working with the semiconductor, Ye said.

One drawback to the material is that it possesses poor thermal properties. To help solve the problem, future research may include work to attach the material to a substrate of diamond or aluminum nitride.

The research was based at Discovery Park’s Birck Nanotechnology Center.
Source: Purdue University

3 MilliWatt-Consumption Data Glasses

Data glasses display information to the eye without interfering with the wearer‘s vision but they run energy down very quickly due to the consumption of electronics while processing video images and data. Researchers at  Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP had developed a new data glass that has low-power consumption. Received using a radio link, the glasses is able to display images to the wearer while his/her hands are free.

These glasses also goes bright even the power is somehow low thanks to the OLEDs embedded to a silicon semiconductor which controls the individual pixels. Plus, they have the ability to perceive light from the environment around not only emit it.

© Photo Fraunhofer FEP

Another reason to high power consumption in data glasses is loading the data stream, but FEP researchers have came up with a new way to reduce it by changing only objects that are changed and keep the constant ones,

“We now control the chip so that the entire video image is not constantly renewed, rather only that part of the display in which something changes.” – Project manager Philipp Wartenberg “For example, if an actor runs through a room in a movie, only his position changes, not the background. In applications such as a navigation system for cyclists, in which only arrows or metre information is displayed, it is unnecessary in any case to constantly renew the whole picture, to put it simply, we have now adapted the circuit so that it only lets through that portion of the data stream which changes.”

FEP data glasses requires an output of 2-3 milliWatts, a fraction of the output need for ordinary displays – around 200 milliWatts.

The new display was presented at the electronica trade fair in Munich on November 08-11, 2016 and its developers hope to see it used by athletes and private clients. You can read more about it at the press release.