An epiphany struck me last week when I attended the Flash Memory Summit in Santa Clara, California. I had come specifically to attend “A Conversation with Eli Harari” which turned out to be an inspiring affair both from a scientific and entrepreneurial viewpoint.
As I wandered around the glitz and glam of the shiny exhibits beforehand, the thought hit me that this whole industry is built upon a single result from the physics of the late 1920’s, namely Quantum Mechanical Tunneling.
The result is that elemental particles like electrons can get through energy barriers even when the particles’ energies are smaller than the height of the barrier. This effect was described almost simultaneously by George Gamov in Europe, and Edward Condon and Ronald Gurney in Princeton in 1928. The concept describes many phenomena from energy generation in stars, nuclear disintegration, and, yes, NAND Flash program and Erase!
Two physicists, Ralph Fowler and Lothar Nordheim, showed in 1928 that an intense electric field can dramatically enhance the electron emission from a conductor. Fowler’s father-in-law, Ernest Rutherford, discerned the structure of the atom from famous experiments carried out at the University of Manchester around 1910. It was around fifty years later that Eli Harari arrived to study at the same university. He then went on to do a PhD at Princeton 45 years after Condon and Gurney had published on quantum tunneling at the same university.
Eli’s research had to do with charge trapping in oxides of aluminum and silicon. At the same time, he studied electron tunneling through thin films. The concepts of tunneling and trapping were to play an important role later on.
After his Ph.D., he joined Hughes in Newport Beach, California where, besides publishing further on the conduction, trapping and breakdown of thin oxides of silicon, he invented the first semiconductor device that used Fowler and Nordheim’s tunneling discovery to charge and discharge a floating gate of a MOS transistor.
After a spell at Intel and a bid to start up Wafer Scale Integration, Eli, Sanjay Mehrotra and Jack Yuan founded SanDisk (initially called SunDisk) in 1988. They were joined by systems expert Bob Norman.
Eli’s description of these early days brought to mind Shakespeare’s Henry the Fifth, “We few, we happy few, we band of brothers”. A golden period of creativity took hold. The key inventions were:
- Multi-state flash where multiple electrical bits are stored in a single physical cell;
- Massively parallel multi-state flash programming and program-inhibit;
- System Flash.
The ability to precisely control the tunneling currents and therefore the amount of charge on a floating gate formed the basis of the multi-state inventions.
The tunneling mechanism is not perfect. It creates damage and charge trapping which Eli had seen before. Having a circuit to minimize this damage and to shepherd damaged cells away from the working population is the foundation of system flash.
Eli also emphasized important points for entrepreneurs:
- Strive for the 10X improvement;
- The team is everything;
- Be persistent in the face of ridicule from the competition and from the venture capitalist community;
- Drive to license to any and all competitors since that will lead to more competition and accelerate the creation of more markets.
The linkup with Toshiba, whose NAND invention incorporated Fowler-Nordheim tunneling that Eli had used a decade and a half earlier, magnified the advantages of SanDisk’s creativity to the benefit of us all.
And the rest is, as they say, history.
And afterwards, standing among the clamor of the exhibits hall, it was a good time to reflect on the golden thread linking up early 20th century fundamental physics and the NAND Flash industry. How different it would all be if Eli Harari had not grasped that thread and run with it!
And how appropriate that he was awarded the National Medal of Technology and Innovation from President Barack Obama in 2014. ~ A.W.
