Laser-printed polysilicon transistors on paper

Could improve wearable electronics, lead to trillions of cheap sensors

1 min read
Laser-printed polysilicon transistors on paper
Photo: R. Ishihara and M. Trifunovic/TU Delft

Printed electronics have opened up applications—flexible circuits and rollable displays, to name two—that were impossible with conventional electronics. Usually, printed electronics are created using organic or metal-oxide inks whose electronic properties often pale in comparison to silicon. Now scientists have discovered a new way to print silicon, potentially ousting its erstwhile usurpers.

The ability to print silicon onto substrates has existed for some time, but producing solid silicon from liquid polysilane ink required exposing the silicon to temperatures upwards of 350 degrees Celsius—far too hot for many of the flexible surfaces onto which one might want to print. The new technique, from Delft University of Technology in the Netherlands and the Japan Advanced Institute of Science and Technology in Ishikawa, completely bypasses this step. The collaborators detailed their findings in the 21 April online edition of the journal Applied Physics Letters.

First, the researchers coated paper with liquid polysilane by skimming the fluid onto the surface with a blade in a virtually oxygen-free, water-free environment. They next transformed this ink into polycrystalline silicon with a blast from an excimer laser, a tool commonly used for manufacturing smartphone displays. The laser pulse only lasted a few dozen nanoseconds, leaving the paper completely intact.

The final silicon film, which is about 200 nanometers thick, required “baking” at a maximum temperature of only 150 °C. The researchers found that the thin-film transistors they created using this new strategy performed on par with conventional polysilicon devices and far better than other ink materials.

The researchers say this work could lead to low-cost, high-speed, flexible, biodegradable, recyclable electronics that could show up in wearable electronics, solar cells, RFID tags, edible devices, and trillions of Internet of Things sensor nodes.

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3 Ways 3D Chip Tech Is Upending Computing

AMD, Graphcore, and Intel show why the industry’s leading edge is going vertical

8 min read
A stack of 3 images.  One of a chip, another is a group of chips and a single grey chip.
Intel; Graphcore; AMD

A crop of high-performance processors is showing that the new direction for continuing Moore’s Law is all about up. Each generation of processor needs to perform better than the last, and, at its most basic, that means integrating more logic onto the silicon. But there are two problems: One is that our ability to shrink transistors and the logic and memory blocks they make up is slowing down. The other is that chips have reached their size limits. Photolithography tools can pattern only an area of about 850 square millimeters, which is about the size of a top-of-the-line Nvidia GPU.

For a few years now, developers of systems-on-chips have begun to break up their ever-larger designs into smaller chiplets and link them together inside the same package to effectively increase the silicon area, among other advantages. In CPUs, these links have mostly been so-called 2.5D, where the chiplets are set beside each other and connected using short, dense interconnects. Momentum for this type of integration will likely only grow now that most of the major manufacturers have agreed on a 2.5D chiplet-to-chiplet communications standard.

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