Building Better Qubits

This IBM Fellow is researching ways to make the quantum bits faster

4 min read
A photo of a woman in glasses and blue jacket standing in front of a monitor.
IBM

While growing up in Germany, Heike Riel helped her father design and build furniture in the family workshop. She says the experience taught her that “precision and creativity are necessary to build something excellent.”

“Working as a furniture maker was actually a very nice experience because you built something that is high quality and lasts,” Riel says. “When I go back to my hometown, many of our clients still have the furniture that I helped build for them.”


Woodworking also instilled in her a passion for mathematics and physics, she says, adding that she knew she someday would pursue a career in one of those fields.

Today the IEEE senior member is head of science and technology at IBM Research in Zurich. She is also the lead for IBM Research Quantum Europe and Africa, a group that aims to create technologies in artificial intelligence, nanotechnology, quantum computing, and related fields.

The IBM Fellow has helped develop several groundbreaking technologies including OLED displays. She has conducted research in semiconducting nanowires and other nanostructures, as well as molecular electronics. She has authored more than 150 publications and holds more than 60 patents.

Riel is the recipient of this year’s IEEE Andrew S. Grove Award “for contributions to materials for nanoscale electronics and organic light-emitting devices.” The award is sponsored by the IEEE Electron Devices Society.

“I couldn't believe that I was selected [to receive] this very prestigious award,” Riel says. “I feel very humbled and honored because I have great respect for Andrew S. Grove, who was a true technical and business leader in the semiconductor industry, and many people I admire have received this award.”

THE FIRST OLED DISPLAY

After completing a woodworking apprenticeship in 1989, Riel decided to pursue a master’s degree in physics. She graduated in 1997 from Friedrich-Alexander-Universität Erlangen-Nürnberg, in Germany. She joined IBM Research in Zurich in 1998 while pursuing her doctorate in physics in collaboration with the University of Bayreuth, also in Germany.

Her research focused on the optimization of multilayer organic light-emitting devices to be used in displays. After earning her Ph.D. in 2003 she worked at the lab as a research staff member. Riel’s research helped explain the physics behind charge transport and recombination, which govern the operation of all electronic devices, as well as light outcoupling in organic semiconductors.

“Back then, people didn’t believe it could be done, but that didn’t stop us.”

Her findings helped improve the efficiency, color, and endurance of OLEDs, which made it possible for her and the team to develop the first 51-centimeter full-color active-matrix OLED display. The technology is made by placing thin films of light-emitting organic compounds between two conductors. When voltage is applied, a bright light is emitted from each individual pixel. OLEDs can be found in TV screens, tablets, and smartphones.

“We had one year to scale organic LEDs to make a 20-inch display in three different colors with pixel sizes of 100 micrometers by 300 micrometers,” Riel said in a 2021 interview for IBM’s Research blog. “Back then [in the early 2000s], people didn’t believe it could be done, but that didn’t stop us.”

She says it’s rewarding to have developed something consumers use every day.

“When my husband bought our first OLED television, it was really exciting,” she recalls. “Suddenly I owned a product that is using technologies I developed.”

NANOWIRE TRANSISTORS

Riel went on to become head of IBM’s nanoscale electronics group, which develops semiconducting nanowires and nanostructures for transistors. She and her team helped develop the first vertical surround-gate nanowire field-effect transistor in 2006.

Researchers around the world had been trying to reduce the size of transistors for decades. But each time the transistors were miniaturized, their performance decreased; eventually they couldn’t effectively control electric current.

“It became clear,” Riel says, “that how we built transistors had to change in the early 2000s.”

“We had to come up with new ideas for how to improve the quality of [transistors] when we make them smaller,” she says. “We explored and developed new materials and integration schemes for nanoscale electronics and new transistor architectures based on semiconducting nanowires.”

Riel and her team implemented gate-all-around and cylindrical nanowires for transistors. Because the nanowires are cylindrical, the transistor gate can be wrapped around the nanowires—which allows better control of the current, according to a research paper authored by Riel and her colleagues.

In 2017 IBM released a new transistor—the Nanosheet—that uses the concepts Riel says she and her team developed between 2005 and 2012. Each transistor is made up of three stacked horizontal silicon sheets, each a few nanometers thick and completely surrounded by a gate. Last year IBM unveiled the world’s first 2-nm node chip, which was based on Nanosheet technology.

“IBM claims this new chip will improve performance by 45 percent using the same amount of power, or use 75 percent less energy while maintaining the same performance level, as today’s 7 nm-based chips,” anIEEE Spectrum article said.

ENHANCING THE QUBIT

Riel is currently conducting quantum-computing research. She and her team are developing qubits and related technologies.

Classical computers switch transistors on and off to represent data as ones or zeros. Because of the nature of quantum physics, qubits can be in a state of superposition, whereby they are both 1 and 0 simultaneously, as explained in a 2020 IEEE Spectrum article. Quantum computers can perform some tasks far faster and more accurately than conventional machines.

“We are trying to figure out whether a new material would make them function better and if [certain materials] could have advantages over today’s processors,” Riel says. Her team has been experimenting with silicon spin qubits and topological phenomena.

She and her team are taking a holistic approach, she says, and are building a quantum system from the ground up—creating the qubit, quantum processor unit technology, control electronics, and software. In November the IBM team demonstrated the Eagle, a 127-qubit chip: the world’s first quantum processor to break the 100-qubit barrier.

Her team also is working to find a good way to connect two quantum processors. In quantum computing, she says, transduction is necessary to transport information over a long distance from one processor to another. Quantum transduction is the process of converting quantum signals from a low-energy photon to a high-energy photon to protect its state during transmission.

“To do this conversion, you need sophisticated technology,” Riel says. “We are exploring different approaches and figuring out which is the best and how we can achieve the specifications that you need for doing it.”

CONNECTING THROUGH IEEE

Riel says she joined IEEE in 2007 so she could contribute to the community, participate in conferences, and connect with other engineers.

A member of the IEEE Electron Devices Society, she has helped to organize events including the IEEE European Solid-State Device Research Conference, the IEEE International Electron Devices Meeting, and the IEEE Symposium on VLSI Technology and Circuits.

Riel says IEEE has enriched her career, allowing her to keep up with technology advances and to network with peers.

The Conversation (1)
Abdo Eid08 Jan, 2022
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The Inner Beauty of Basic Electronics

Open Circuits showcases the surprising complexity of passive components

5 min read
Vertical
A photo of a high-stability film resistor with the letters "MIS" in yellow.
All photos by Eric Schlaepfer & Windell H. Oskay
Blue

Eric Schlaepfer was trying to fix a broken piece of test equipment when he came across the cause of the problem—a troubled tantalum capacitor. The component had somehow shorted out, and he wanted to know why. So he polished it down for a look inside. He never found the source of the short, but he and his collaborator, Windell H. Oskay, discovered something even better: a breathtaking hidden world inside electronics. What followed were hours and hours of polishing, cleaning, and photography that resulted in Open Circuits: The Inner Beauty of Electronic Components (No Starch Press, 2022), an excerpt of which follows. As the authors write, everything about these components is deliberately designed to meet specific technical needs, but that design leads to “accidental beauty: the emergent aesthetics of things you were never expected to see.”

From a book that spans the wide world of electronics, what we at IEEE Spectrum found surprisingly compelling were the insides of things we don’t spend much time thinking about, passive components. Transistors, LEDs, and other semiconductors may be where the action is, but the simple physics of resistors, capacitors, and inductors have their own sort of splendor.

High-Stability Film Resistor

A photo of a high-stability film resistor with the letters "MIS" in yellow.

All photos by Eric Schlaepfer & Windell H. Oskay

This high-stability film resistor, about 4 millimeters in diameter, is made in much the same way as its inexpensive carbon-film cousin, but with exacting precision. A ceramic rod is coated with a fine layer of resistive film (thin metal, metal oxide, or carbon) and then a perfectly uniform helical groove is machined into the film.

Instead of coating the resistor with an epoxy, it’s hermetically sealed in a lustrous little glass envelope. This makes the resistor more robust, ideal for specialized cases such as precision reference instrumentation, where long-term stability of the resistor is critical. The glass envelope provides better isolation against moisture and other environmental changes than standard coatings like epoxy.

15-Turn Trimmer Potentiometer

A photo of a blue chip
A photo of a blue chip on a circuit board.

It takes 15 rotations of an adjustment screw to move a 15-turn trimmer potentiometer from one end of its resistive range to the other. Circuits that need to be adjusted with fine resolution control use this type of trimmer pot instead of the single-turn variety.

The resistive element in this trimmer is a strip of cermet—a composite of ceramic and metal—silk-screened on a white ceramic substrate. Screen-printed metal links each end of the strip to the connecting wires. It’s a flattened, linear version of the horseshoe-shaped resistive element in single-turn trimmers.

Turning the adjustment screw moves a plastic slider along a track. The wiper is a spring finger, a spring-loaded metal contact, attached to the slider. It makes contact between a metal strip and the selected point on the strip of resistive film.

Ceramic Disc Capacitor

A cutaway of a Ceramic Disc Capacitor
A photo of a Ceramic Disc Capacitor

Capacitors are fundamental electronic components that store energy in the form of static electricity. They’re used in countless ways, including for bulk energy storage, to smooth out electronic signals, and as computer memory cells. The simplest capacitor consists of two parallel metal plates with a gap between them, but capacitors can take many forms so long as there are two conductive surfaces, called electrodes, separated by an insulator.

A ceramic disc capacitor is a low-cost capacitor that is frequently found in appliances and toys. Its insulator is a ceramic disc, and its two parallel plates are extremely thin metal coatings that are evaporated or sputtered onto the disc’s outer surfaces. Connecting wires are attached using solder, and the whole assembly is dipped into a porous coating material that dries hard and protects the capacitor from damage.

Film Capacitor

An image of a cut away of a capacitor
A photo of a green capacitor.

Film capacitors are frequently found in high-quality audio equipment, such as headphone amplifiers, record players, graphic equalizers, and radio tuners. Their key feature is that the dielectric material is a plastic film, such as polyester or polypropylene.

The metal electrodes of this film capacitor are vacuum-deposited on the surfaces of long strips of plastic film. After the leads are attached, the films are rolled up and dipped into an epoxy that binds the assembly together. Then the completed assembly is dipped in a tough outer coating and marked with its value.

Other types of film capacitors are made by stacking flat layers of metallized plastic film, rather than rolling up layers of film.

Dipped Tantalum Capacitor

A photo of a cutaway of a Dipped Tantalum Capacitor

At the core of this capacitor is a porous pellet of tantalum metal. The pellet is made from tantalum powder and sintered, or compressed at a high temperature, into a dense, spongelike solid.

Just like a kitchen sponge, the resulting pellet has a high surface area per unit volume. The pellet is then anodized, creating an insulating oxide layer with an equally high surface area. This process packs a lot of capacitance into a compact device, using spongelike geometry rather than the stacked or rolled layers that most other capacitors use.

The device’s positive terminal, or anode, is connected directly to the tantalum metal. The negative terminal, or cathode, is formed by a thin layer of conductive manganese dioxide coating the pellet.

Axial Inductor

An image of a cutaway of a Axial Inductor
A photo of a collection of cut wires

Inductors are fundamental electronic components that store energy in the form of a magnetic field. They’re used, for example, in some types of power supplies to convert between voltages by alternately storing and releasing energy. This energy-efficient design helps maximize the battery life of cellphones and other portable electronics.

Inductors typically consist of a coil of insulated wire wrapped around a core of magnetic material like iron or ferrite, a ceramic filled with iron oxide. Current flowing around the core produces a magnetic field that acts as a sort of flywheel for current, smoothing out changes in the current as it flows through the inductor.

This axial inductor has a number of turns of varnished copper wire wrapped around a ferrite form and soldered to copper leads on its two ends. It has several layers of protection: a clear varnish over the windings, a light-green coating around the solder joints, and a striking green outer coating to protect the whole component and provide a surface for the colorful stripes that indicate its inductance value.

Power Supply Transformer

A photo of a collection of cut wires
A photo of a yellow element on a circuit board.

This transformer has multiple sets of windings and is used in a power supply to create multiple output AC voltages from a single AC input such as a wall outlet.

The small wires nearer the center are “high impedance” turns of magnet wire. These windings carry a higher voltage but a lower current. They’re protected by several layers of tape, a copper-foil electrostatic shield, and more tape.

The outer “low impedance” windings are made with thicker insulated wire and fewer turns. They handle a lower voltage but a higher current.

All of the windings are wrapped around a black plastic bobbin. Two pieces of ferrite ceramic are bonded together to form the magnetic core at the heart of the transformer.

This article appears in the February 2023 print issue.

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