Research Bits: July 11

ALE modeling

Scientists from the Princeton Plasma Physics Laboratory (PPPL) of the United States Department of Energy (DOE), in coordination with Lam Research, modeled atomic layer etching (ALE) for the manufacture of semiconductors.

“It would be a small piece in the whole process,” said David Graves, associate laboratory director for low-temperature plasma surface interactions at PPPL and professor in the Department of Chemical and Biological Engineering at Princeton. Knowledge gained from modeling, he said, “can lead to all sorts of good things, and that’s why this effort in the lab is promising.”

“The simulations were essentially in agreement with the experiments initially and could lead to a better understanding of the use of ALE for atomic-scale etching,” said Joseph Vella, postdoctoral fellow at PPPL. He added that a better understanding will allow PPPL to study things like the extent of surface damage and the degree of roughness developed during FTA.

The model simulated the sequential use of chlorine gas and argon plasma ions to control the atomic-scale silicon etching process. Plasma, or ionized gas, is a mixture of free electrons, positively charged ions and neutral molecules. The plasma used in processing semiconductor devices is near room temperature, unlike the ultra-hot plasma used in fusion experiments.

“A surprising empirical finding from Lam Research was that the ALE process became particularly efficient when the ion energies were somewhat higher than what we started with,” Graves said. “So that will be our next step in the simulations – to see if we can figure out what happens when the ion energy is much higher and why it’s so good.”

Network of switches for lidar chip

Engineers at the University of California, Berkeley have built a high-resolution lidar (light detection and ranging) chip based on a focal plane switch array (FPSA), a semiconductor-based antenna array that collects light like sensors in digital cameras.

The 16,384 pixel resolution on a 1 square centimeter chip is a big increase over the 512 pixels or less found on FPSAs so far. It is also scalable up to megapixel sizes using CMOS technology.

The Lidar works by capturing the reflections of the light emitted by its laser. Achieving the power and resolution available in a large, mechanically rotated lidar in a chip form factor has proven challenging.

“We want to illuminate a very large area,” said Ming Wu, professor of electrical engineering and computer science and co-director of the Berkeley Sensor and Actuator Center at the University of California, Berkeley. “But if we try to do that, the light becomes too weak to reach a sufficient distance. So, as a design compromise to maintain light intensity, we reduce the areas we illuminate with our laser light. »

The FPSA contributes to this. It consists of an array of tiny optical transmitters, or antennas, and switches that quickly turn them on and off. This way it can channel all available laser power through a single antenna at a time.

Switching, however, poses a problem. Thermo-optical switches are commonly used in lidar chips, but large numbers together can generate too much heat to function properly. Instead, the team adopted MEMS switches that physically move the waveguides from one position to another.

“The construction is very similar to a freeway interchange,” Wu said. “So imagine you’re a beam of light going from east to west. We can mechanically lower a ramp that will suddenly turn you 90 degrees , so you are going from north to south.

When the switch turns on a pixel, it emits a laser beam and picks up the reflected light. Each pixel is equivalent to 0.6 degrees of the 70 degree field of view of the array. By rapidly traversing the network, the FPSA constructs a 3D image of the world around it. Mounting several of them in a circular configuration would produce a 360 degree view around a vehicle.

A further increase in FPSA resolution is needed for commercialization, Wu said. “Although it is difficult to reduce the size of optical antennas, switches are still the largest components and we believe we can reduce them much more.”

Increasing range from the current iteration’s 10 meters would also be required. “We are confident we can get to 100 meters and believe we can get to 300 meters with continued improvement,” he said.

Wu thinks lidar won’t be limited to automotive applications. “Just look at how we use the cameras. They are integrated into vehicles, robots, vacuum cleaners, surveillance equipment, biometrics and doors. There will be so many more potential applications once we get lidar down to the size of a smartphone camera. »

Stretch without distortion

Researchers from the Korea Institute of Machinery and Materials (KIMM) have developed a expandable micro-LED meta-display which can be stretched up to 25% without image distortion.

As a general rule, stretchy materials like rubber will deform, shrinking in one direction when pulled in the other. The new 3-inch screen uses mechanical metamaterials with negative Poisson’s ratio, which have been applied to a circuit board. Poisson’s ratio refers to the ratio at which the width of the material shrinks when stretched lengthwise. When a mechanical metamaterial with a Poisson’s ratio of -1 is stretched lengthwise, it demonstrates the effect of stretching at the same ratio in the widthwise direction.

It can be fabricated by transferring a micro-LED device onto a large-area meta-circuit board using roller-based large-area transfer technology. After the micro-LED transfer, the meta-display is fabricated by reflow and the board cut into a kirigami pattern using a laser, which allows for stretching.

In demonstrations, the screen was attached to a hemispherical surface with a radius of 80 cm without wrinkles or creases, which made it possible to build screens that could be attached to the skin and conformed to the human body.

The team plans to continue follow-up research and study applications in mini-LEDs and graphene, as well as further commercialization.

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