IMEC, a world-leading independent
research center in nanoelectronics and nanotechnology, and its 3D integration
partners have taped-out Etna, a new 3D chip integrating a commercial DRAM chip
on top of a logic IC. The new 3D stack resembles as close as possible to future
commercial chips. It consists of a 25µm thick logic die on top of which
a commercial DRAM is stacked using through-silicon vias (TSVs) and micro-bumps.
ETNA 3D chip stack paving the way for DRAM on logic integration;
(top) stack configuration; (bottom) layout of the logic die
The 3D demonstrator mimics all aspects of the approach by stacking an advanced
commercial DRAM product chip on IMEC’s proprietary CMOS logic IC. As an
example, heaters are integrated to test the impact of hotspot on DRAM refresh
times. And, the chip contains test structures for monitoring thermo-mechanical
stress in a 3D stack, ESD (electro-static discharge) hazards, electrical characteristics
of TSVs and micro-bumps, fault models for TSVs, etc.
The design of the 3D chip is realized together with many players in the 3D
integration supply chain. Now, IMEC is manufacturing the logic die in its prototype
line, and will be stacking the commercial DRAM chip on top of it. One of IMEC’s
3D integration partners will deliver the DRAM dies, and will test the fabricated
3D stack; two other partners, will package the 3D stack using flip-chip onto
a FBGA (fine-pitch ball-grid array) substrate.
“We are excited to achieve this milestone in collaboration with our 3D
integration partners including memory suppliers and IC manufacturers. This test-chip
is a significant step for the introduction of 3D technology in DRAM-on-logic
applications;” said Pol Marchal, principal scientist 3D integration at