Nantero

Nantero was founded in 2001, and headquartered in Woburn, Massachusetts. Due to the massive investment in flash semiconductor fabrication plants, no alternative memory has replaced flash in the marketplace, despite predictions as early as 2003 of the impending speed and density of NRAM.

In 2005, NRAM was promoted as universal memory, and Nantero predicted it would be in production by the end of 2006.

In August 2008, Lockheed Martin acquired an exclusive license for government applications of Nantero's intellectual property.

By early 2009, Nantero had 30 US patents and 47 employees, but was still in the engineering phase. In May 2009, a radiation-resistant version of NRAM was tested on the STS-125 mission of the US Space Shuttle Atlantis.

The company was quiet until another round of funding and collaboration with the Belgian research center imec was announced in November 2012.

Nantero raised a total of over $42 million through the November 2012 series D round.

Investors included Charles River Ventures, Draper Fisher Jurvetson, Globespan Capital Partners, Stata Venture Partners and Harris & Harris Group.

In May 2013, Nantero completed series D with an investment by Schlumberger.

The first generation Nantero NRAM technology was based on a three-terminal semiconductor device where a third terminal is used to switch the memory cell between memory states. The second generation NRAM technology is based on a two-terminal memory cell. The two-terminal cell has advantages such as a smaller cell size, better scalability to sub-20 nm nodes (see semiconductor device fabrication), and the ability to passivate the memory cell during fabrication.

In a non-woven fabric matrix of carbon nanotubes (CNTs), crossed nanotubes can either be touching or slightly separated depending on their position. When touching, the carbon nanotubes are held together by Van der Waals forces. Each NRAM "cell" consists of an interlinked network of CNTs located between two electrodes as illustrated in Figure 1. The CNT fabric is located between two metal electrodes, which is defined and etched by photolithography, and forms the NRAM cell.

The NRAM acts as a resistive non-volatile random-access memory (RAM) and can be placed in two or more resistive modes depending on the resistive state of the CNT fabric. When the CNTs are not in contact the resistance state of the fabric is high and represents an "off" or "0" state. When the CNTs are brought into contact, the resistance state of the fabric is low and represents an "on" or "1" state. NRAM acts as a memory because the two resistive states are very stable. In the 0 state, the CNTs (or a portion of them) are not in contact and remain in a separated state due to the stiffness of the CNTs resulting in a high resistance or low current measurement state between the top and bottom electrodes. In the 1 state, the CNTs (or a portion of them) are in contact and remain contacted due to Van der Waals forces between the CNTs, resulting in a low resistance or high current measurement state between the top and bottom electrodes. Note that other sources of resistance such as contact resistance between electrode and CNT can be significant and also need to be considered.

To switch the NRAM between states, a small voltage greater than the read voltage is applied between top and bottom electrodes. If the NRAM is in the 0 state, the voltage applied will cause an electrostatic attraction between the CNTs close to each other causing a SET operation. After the applied voltage is removed, the CNTs remain in a 1 or low resistance state due to physical adhesion (Van der Waals force) with an activation energy (Ea) of approximately 5eV. If the NRAM cell is in the 1 state, applying a voltage greater than the read voltage will generate CNT phonon excitations with sufficient energy to separate the CNT junctions. This is the phonon driven RESET operation. The CNTs remain in the OFF or high resistance state due to the high mechanical stiffness (Young's Modulus 1 TPa) with an activation energy (Ea) much greater than 5 eV. Figure 2 illustrates both states of an individual pair of CNTs involved in the switch operation. Due to the high activation energy (> 5eV) required for switching between states, the NRAM switch resists outside interference like radiation and operating temperature that can erase or flip conventional memories like DRAM.