Vertical Cross-point Memory
VCMTM (Vertical Cross-point Memory) Bit Cell Technology
Kilopass’s new Vertical Cross-point Memory (VCM) bit cell is a breakthrough technology that quadruples memory capacity over today’s antifuse NVM bit cell technology for embedding non-volatile data in system-on-chip (SoC) products. The VCM bit cell technology differs from that of the current Kilopass eNVM IP, which requires a lateral selection transistor in planar (X-Y) directions to form memory bits. The VCM bit cell technology uses one single P-MOS transistor to both store and control the memory content. This compaction method reduces the footprint of the single bit cell from about 75 F2 for Kilopass’ current XPM memory to 12 F2 for VCM memory, where each F describes a manufacturable feature. By comparison, a typical embedded flash memory has an area of about 50 F2, and the state-of-the-art NAND flash bit cell with a fully customized memory process technology and extra cost can only achieve 6F2, about half of the area of the VCM bit cell. The VCM bit cell is truly the densest eNVM that exists in standard logic process.
VCM bit cell technology does require a simple added processing step/mask, but needs no new materials, equipment, or additional thermal cycles. An additional mask is used, which is relatively coarse grade and is inexpensive and easy to manufacture. Indeed, the VCM bit cell memory technology has been designed into a 110nm analog/mixed signal process in three different test shuttles with successful results. VCM bit cell technology is currently ready to be integrated into the upcoming NumeraTM product in early 2013.
The VCM bit cell memory technology fills an eNVM void not addressed by external components such as serial-flash/EEPROM, Read-only Memory (ROM), and embedded flash (eFlash).
Today’s external serial EEPROM or serial Flash with an on-chip shadow SRAM is untenable because of power and cost constraints. The Embedded flash alternative is not available at process nodes below 65nm and even when available may add too much cost to a predominantly logic SoC. The read-only memory (mask-ROM) alternative comes with the drawback of having to be configured during design and any program change requiring an expensive and lengthy design re-spin. The VCM bit cell provides an attractive alternative to all three of these solutions that overcomes their shortcomings. It reduces the bill of materials cost and logistics requirement of an external EEPROM and replaces the associated embedded shadow SRAM function in an equivalent silicon area. The memory is a small fraction of the cost of embedded EEPROM or flash and is built on Kilopass’ proven, scalable, anti-fuse technology foundation. It adds the flexibility not possible with ROM of being programmable at final test and reprogrammable in the field if program changes are required.
Kilopass will initially target the ultra-low power, high integration wireless devices built in 55nm to 40nm technologies, where the MCU-like SOC requires extended battery life, small form factor, and execute-in-place performance, all ideal for the VCM bit cell technology. In addition, these devices often require different software versions and updates, which make the VCM memory technology superior to mask based memory like ROM.