Research Bits: Feb. 6

Pillars for chiplet integration

Researchers from the Tokyo Institute of Technology proposed a new chiplet integration technology called Pillar-Suspended Bridge (PSB), which they say is a simpler method of chip-to-chip connection compared to silicon interposers and redistribution layers.

In the PSB, only a pillar-shaped metal structure called a “MicroPillar” is interposed at the connection between the chiplet and the silicon bridge. The chiplets are sealed with mold resin together with the bridge, and is connected to an external electrode by a “Tall Pillar” penetrating the mold on the silicon bridge side.

The researchers said that this structure makes it possible to improve the inter-chip connection density and electrical properties by minimizing the chiplet/bridge interconnect element, and to improve the high-frequency properties of the external connection wiring and heat dissipation performance.

They also note that there is no yield problem when scaling up integration and that the size and manufacturing units of the integrated module can be expanded to large panels.

An All Chip-last process was used to create high bonding accuracy and reduce die shift during the manufacturing process, along with a bonding process with matching linear expansion.

The team said that the PSB structure has a simple structure for chiplet integration using a silicon bridge. They found that by connecting a wiring layer with a Fan-Out function, it was possible to assemble either a chiplet integrated package or a large-scale chiplet integrated system.

Next, they plan to increase interconnection density and scale up integration, develop high-performance bridge wiring technology and global wiring integration technology, verify reliability, and verify system applications.

Disposable papertronics

Researchers from Binghamton University created a prototype circuit board that is made out of a sheet of paper with fully integrated electrical components, and that can be burned or left to degrade.

The team designed a paper-based amplifier-type circuit that incorporated resistors, capacitors, and a transistor. They first used wax to print channels onto a sheet of paper in a simple pattern. After melting the wax so that it soaked into the paper, the team printed semiconductive and conductive inks, which soaked into the areas not blocked by wax. Then, the researchers screen-printed additional conductive metal components and casted a gel-based electrolyte onto the sheet.

Tests confirmed that the resistor, capacitor, and transistor designs performed properly. The final circuit was flexible and thin, even after adding the components. To demonstrate the degradability of the circuit, the team showed that the entire unit quickly burned to ash after being lit on fire. The researchers say this represents a step toward producing completely disposable electronic devices.

Switchable EMI shielding

A MXene-based thin film device, fabricated by spray coating, that can block electromagnetic radiation was developed by researchers at Drexel University. They say it could be used to adjust the performance of electronic devices, strengthen wireless connections, and secure mobile communications against intrusion.

“Dynamic control of electromagnetic wave jamming has been a significant technological challenge for protecting electronic devices working at gigahertz frequencies and a variety of other communications technologies,” said Yury Gogotsi, a professor in Drexel’s College of Engineering.

MXene is unique in that it is highly conductive, but its internal chemical structure can also be temporarily altered to allow electromagnetic waves to pass through. This would allow a thin coating to prevent a device from both emitting electromagnetic waves as well as being penetrated by those emitted by other electronics. But the shielding property is bidirectionally tunable by using the flow and expulsion of ions to alternately expand and compress the space between material’s layers.

When a small voltage is applied to the film, ions enter – or intercalate – between the MXene layers altering the charge of their surface and inducing electrostatic attraction, which serves to change the layer spacing, the conductivity and shielding efficiency of the material. When the ions are deintercalated, as the current is switched off, the MXene layers return to their original state.

“Without being able to control the ebb and flow of electromagnetic waves within and around a device, it’s a bit like a leaky faucet – you’re not really turning off the water and that constant dripping is no good,” Gogotsi said. “Our shielding ensures the plumbing is tight – so-to-speak – no electromagnetic radiation is leaking out or getting in until we want to use the device.”

The team tested 10 different MXene-electrolyte combinations, applying each via paint sprayer in thin layers. The materials consistently demonstrated the dynamic tunability of shielding efficiency in blocking microwave radiation. The device sustained the performance through more than 500 charge-discharge cycles.

They also tested the potential of a one-way shielding switch. This would allow a device to remain undetectable and protected from unauthorized access until it is deployed for use. “A one-way switch could open the protection and allow a signal to be sent or communication to be opened in an emergency or at the required moment,” Gogotsi said. “This means it could protect communications equipment from being influenced or tampered with until it is in use. For example, it could encase the device during transportation or storage and then activate only when it is ready to be used.”

Next, the team plans to explore additional MXene-electrolyte combinations and mechanisms to fine-tune the shielding to achieve a stronger modulation of electromagnetic wave transmission and dynamic adjustment to block radiation at a variety of bandwidths.