Technology

IMSI's roadmap is somewhat different from others. Rather than extending conventional technologies, our proposals faithfully follow the physical laws and material properties of nature, and are therefore based on essentially simple principles and structures.

■ We propose wiring and interconnect structures based on paired lines, grounded in the laws of electromagnetism and plasmonic considerations.
→ By raising the frequency while maintaining basic binary transmission, high-speed signal transmission is achieved with simple I/O interfaces.

■ We propose room-temperature bonding that exploits the surface activity of solid materials.
→ The surface activation process lowers the bonding temperature and achieves ideal direct bonding without unnecessary interfacial layers, with high reliability and at low cost.

High-speed signal transmission using paired lines

Since its foundation, IMSI has studied high-speed signal transmission by returning to the fundamental principles of electromagnetism and solid-state physics. Based on the essential fact that electrical energy flows as electromagnetic energy at the speed of light only when a pair of lines is present, IMSI proposed wiring and interconnect structures that confine signals within paired lines, and demonstrated transmission of 6 Gbps over 400 mm on an FR-4 board and 1 Gbps over 100 m of Ethernet cable per line pair.

· Pursuit of distributed parallel processing based on increased wiring counts and 3D matrix devices, together with ultra-high-speed signal transmission.
· A path toward a "memory-logic conjugate system" that combines memory and logic, through integration with bumpless interconnect technology.
· These results have been compiled into design guidelines for high-speed signal processing covering SI (signal integrity) and PI (power integrity).

Surface Activated Bonding (SAB) is a unique bonding method in which material surfaces are cleaned and activated in vacuum and then simply brought into contact at room temperature to form a strong bond. It can be applied not only to metals but also to a wide variety of materials, including semiconductors, ceramics and plastics. In recent years, bonding in ambient air has also become possible.

Room-temperature bonding is no longer a dream

Room-temperature bonding as a practical, mass-production technology

· Depending on the conditions, bonding in ambient air is also possible, and room-temperature processing enables high throughput.
· Mass-production equipment is now commercially available from IMSI member equipment manufacturers.

Proposals for pioneering new processes

· In addition to semiconductors and metals, polymer films and glass can now be bonded, and hybrid bonding of these materials with metals and semiconductors has become possible.
· We are also developing high-temperature reversible interconnects that are formed at room temperature, withstand high-temperature processing and can be debonded at room temperature.

Expanding fields of application

· In semiconductors and microelectronics, practical use and mass production have begun in low-temperature bonding for 3D integration, component manufacturing by bonding piezoelectric single-crystal substrates, and MEMS packaging.
· Applications are also advancing in multi-junction solar cells, Si photonics devices, power modules and the encapsulation of organic EL displays.

Bumpless interconnect (2000 and 2008)

Global interconnect: the origin of the 2.5D packaging concept using chiplets (2001)

Room-temperature Cu-Cu direct bonding by Surface Activated Bonding (SAB) (2003)

Extensions of surface activated bonding

Atomic Diffusion Bonding (ADB)

· In ultra-high vacuum, ultra-thin metal or inorganic films a few nanometers thick are sputter-deposited onto the surfaces of the two substrates, which are then brought into contact without breaking the vacuum. Atomic diffusion at the film interface and grain boundaries produces a strong bond at room temperature.
· Bonding is possible with a variety of metal films such as Ti, Au and Pt, as well as oxide and nitride films, regardless of the substrate material and uniformly over the entire wafer.
· By making the films extremely thin, transparent bonds with almost no optical absorption can be obtained, and applications are advancing in optical devices, piezoelectric devices and wafer-level sealing of MEMS.
· IMSI regards ADB as a leading room-temperature bonding method alongside SAB and pursues research on both as complementary technologies.

Cu-Cu bonding by Atomic Diffusion Bonding (ADB) in ultra-high vacuum

Modified SAB

· Beyond oxide removal by ion bombardment, low-temperature bonding under atmospheric pressure (below 200 °C) has become possible using formic acid activation with a platinum catalyst.
· Combining the exposure of dangling bonds by ion bombardment with hydrophilization has enabled low-temperature bonding in ambient air (below 200 °C).
· By introducing intermediate layers of Au or Si (nano-adhesion layers), room-temperature bonding has been extended to glass and polymer films.

What is cryogenic bonding?

· Conventionally, bonding below 200 °C, that is, above room temperature but below soldering temperatures or the temperatures at which thermal diffusion bonding of Cu becomes difficult, has been called "low-temperature bonding". Recently, however, it has been found that surface activation enables direct bonding even below room temperature, at liquid-nitrogen temperature. This shows that literally "cryogenic bonding" is possible, and elucidation of its mechanism is anticipated.

Heterogeneous integration, the integration of dissimilar chips, is one of the hottest topics in packaging today. In AI data centers and automotive inverters in particular, next-generation power devices such as SiC and GaN are becoming essential for higher power density and lower losses.

These wide-bandgap (WBG) devices offer fast switching and enable major reductions in loss and size. To bring out their full performance, however, packaging must achieve both low-inductance wiring and high heat dissipation. Simply applying module structures developed for conventional Si devices cannot fully exploit the characteristics of WBG devices.

Embedded packaging

As a promising solution, "embedded packaging", in which power semiconductors are embedded in printed wiring boards and connected directly with copper wiring, is attracting considerable attention. Compared with conventional Si devices, however, practical implementation requires comprehensive study of packaging technologies, including insulation under high voltage, thermal design and the reliability of interconnections.

To address these challenges, IMSI's Power Module WG conducts research on 3D wiring technologies, high-heat-dissipation composite substrates and the heat-resistant materials and components needed to build them, as well as on making power modules intelligent through sensor technologies so that they operate optimally as systems.