Stacked Memory Packaging Technology Takes Mobile Memory Design to New Level
Single Package Can House Eight Memory Chips and One Controller Chip
KAWASAKI, Japan, Dec. 11 // -- NEC Electronics, working jointly with Elpida Memory and Oki Electric, has developed novel packaging technology that will allow cell phones and other portable devices to be equipped with as much memory as a high-performance computer. The new technology places eight memory chips and one controller chip in a vertical stack, with three- dimensional (3D) connections between the chips, providing enough memory for demanding high-definition video and high-speed 3D graphics applications in a package slim enough for cell phones and portable game players.
The key feature of the new technology is the way that chips in the stack are connected. Each chip has more than 1,000 pins on each side. The pins are connected to polysilicon electrodes built into the chips themselves, vertically piercing the chips from top to bottom. The chips are then connected to each other by high-density microbumps spaced only 50 micrometers (um) apart. The entire package, including the controller chip, is very compact because each of the eight memory chips is only 50 um thick.
From PCs and network servers to digital music players and cell phones, every type of electronic device needs more memory to support the latest applications. For applications like digital video and 3D games, mobile devices also need faster access to memory and power consumption as low as possible. Chip suppliers have developed a number of ways to meet these requirements. Memory can be built into system-on-chip (SoC) solutions, or included in system-in-package (SiP) solutions. The SiP approach typically involves stacking a number of memory chips over interposers and connecting them to a processor chip by wire bonding. But each of these approaches has its disadvantages. It is difficult to build enough memory into a single SoC chip. The wire bonding in SiP solutions creates impedance balancing problems and limits the number of pins that can be connected to the processor, which makes it difficult to increase the signal speed. Wire bonding also limits the number of chips that can be added to the stack.
In search of a fundamental solution to these problems, NEC Electronics, Elpida Memory and Oki Electric initiated a stacked memory development project in August 2004, supported by a grant from the New Energy and Industrial Technology Development Organization (NEDO). The research focused on packaging innovations and fabrication of the through-chip polysilicon electrodes. Careful optimization of the electrode structure made it possible to achieve high fabrication throughput. Packing innovations included optimization of NEC Electronics' advanced SMAFTI(TM) SiP packing technology for stacked memory. This enabled leading-edge 3D interconnects with an extremely dense 50 um pitch.
The result was the development of packaging technology to allow stacking of eight memory chips and one controller chip with internal microbump connections at the dense pitch of 50 µm. This technology will enable smaller form factors, faster operating speeds and lower power consumption in the next generation of mobile devices. The three companies are committed to further work to enhance the technology and bring it to market as soon as possible.
The results of this research will be announced at the International Electron Devices Meeting 2006 (IEDM 2006), to be held over three days beginning December 11 in San Francisco (USA).
About NEC Electronics
NEC Electronics Corporation specializes in semiconductor products encompassing advanced technology solutions for the high-end computing and broadband networking markets, system solutions for the mobile handset, PC peripherals, automotive and digital consumer markets, and platform solutions for a wide range of customer applications. NEC Electronics Corporation has 24 subsidiaries worldwide including NEC Electronics America, Inc. ( www.am.necel.com/ ) and NEC Electronics (Europe) GmbH ( www.eu.necel.com/ ). For additional information about NEC Electronics worldwide, visit www.necel.com/.
NOTE: SMAFTI is a trademark of NEC Electronics Corporation in Japan, Germany, the Republic of Korea, and Taiwan.
Source: NEC Electronics Corporation
CONTACT: Sophie Yamamoto of NEC Electronics Corporation,
+ 81-44-435-1676, or sophie.yamamoto@necel.com
Web site: www.necel.com/
