How Memristance Works
This document describes the physical mechanics of memristance as it operates in a cross-bar architecture configuration. Memristance is a theoretical concept that has been developed into a physical working mechanism by GALACA Enterpises Electronic Research Laboratories (GEERL) based in Troy, Michigan USA. It bridges the capability gaps that electronics will face in the near future according to Moore’s Law and will replace the transistor as the main component on integrated circuit (IC) chips.
FUNCTION – The function of the memristor is to provide the ability to remember current flow across a resistor permanently. This attribute will allow nano-scale switches to store information on a grand scale using minimal physical space. Test voltages small enough not the affect the resistance could read the data from the memristive circuit. These switching attributes resemble synapse functions in the brain which is a source of intrigue for further development in this area of research. While memristive circuits will never replace the transistor completely due to power factors, they will reduce the size of electronics considerably. The potential for nanoscale crossbar memory in comparison to modern flash technology can be described by placing the entire U.S. Library of Congress on a single thumb drive.
APPEARANCE – Crossbar type memristive circuits contain a lattice of 40-50nm wide by 2-3nm thick platinum wires that are laid on top of one another perpendicular top to bottom and parallel of one another side to side. The top and bottom layer are separated by a switching element approximately 3-30nm in thickness. The switching element consists of two equal parts of titanium dioxide (TiO2). The layer connected to the bottom platinum wire is initially perfect TiO2 and the other half is an oxygen deficient layer of TiO2 represented by TiO2-x where x represents the amount of oxygen deficiencies or vacancies. The entire circuit and mechanism cannot be seen by the naked eye and must be viewed under a scanning tunneling microscope, as seen in Figure 1, in order to visualize the physical set up of the crossbar design of the memristive circuit described in this section.
Figure 1 – View of Crossbar Memristor
OPERATION – The memristor’s operation as a switch can be explained in three steps. These first of these steps is the application of power or more importantly current to the memristor. The second step consists of the amount of time that the current flows across the crossbar gap and how the titanium cube converts from a semi-conductor to a conductor. The final step is the actual memory of the cube that can be read as data.
STEP 1 – As explained above, each gap that connects two platinum wires contains a mixture of two titanium oxide layers. The initial state of the mixture is halfway between conductance and semi-conductance. Two wires are selected to apply power to in either a positive or negative direction. A positive direction will attempt to close the switch and a negative direction will attempt to open the switch. The application of this power will be able to completely open the circuit between the wires but it will not be able to completely close the circuit since the material is still a semi-conductor by nature. Power can be selectively placed on certain wires to open and close the switches in the memristor.
STEP 2 – the second step involves a process that takes place at the atom level and is not visible by any means. It involves the atomic process that the gap material, made from titanium dioxide, goes through that opens and closes the switch. The initial state of the gap is neutral meaning that it consists of one half of pure titanium dioxide TiO2 and one half of oxygen starved titanium dioxide TiO2-x where x in the initial state is 0.05. As positive current is applied, the positively charged oxygen vacancies push their way into the pure TiO2 causing the resistance in the gap material to drop, becoming more conductive, and the current to rise. Inversely, as a negative current is applied the oxygen vacancies withdraw from the pure TiO2 and condense in the TiO2-x half of the gap material causing the pure and more resistive TiO2 to have a greater ratio slowing the current in the circuit. When the current is raised the switch is considered open (HI) and for data purposes a binary 1. As current is reversed and the current is dropped the switch is considered closed (LOW) or a binary 0 for data purposes.
STEP 3 – Step three explains the final step of memristance and is the actual step that makes the circuit memristive in nature. As explained previously, the concept of memristance is a resistor that can remember what current passed through it. When power is no longer applied to the circuit switches, the oxygen vacancies remain in the position that they were last before the power was shut down. This means that the value of the resistance of the material gap will remain until indefinitely until power is applied again. This is the true meaning of memristance. With an insignificant test voltage, one that won’t affect the movement of molecules in the material gap will allow the state of the switches to be read as data. This means that the memristor circuits are in fact storing data physically.
Ritchie for never forgetting where he came from and always promoting Michigan and Detroit to the rest of the world. He started is claim to fame back in the early 90’s but didn’t hit main stream until his release of ‘Devil Without A Cause’ in 1998. I have been a fan since the beginning and was extra excited to see that he was gaining the attention of the
rest of the country. I was at the State Theater for the start of his first solo tour in 1998 and I was 1 of 20-30 people in the upper deck while he filmed his video for the track ‘Bull-God’ for MTV. Last Saturday, 11 years later, I had to settle on watching the show from the giant screens because the tickets sold so fast. Every video I have seen of his has always shown homage to Michigan and especially Detroit and Mt. Clemens. He spent many years as a D.J. in these cities and believes in giving back. His recent endeavor has supported Michigan jobs. He has created a brewery for his own label of beer called BADASS Redneck Lager and the label is representative of his giant tattooed eagle that dorns his upper back. During the concert he took many moments to address the Michigan crowd and show empathy and gratitude for the trying economic times we have and continue to face and the fact that we spent money to come see him. He also took a moment to ask us as fans and Michiganders to join together in times of need and asked the crown to turn to one another and introduce themselves and shake hands. This felt good and really showed his compassion for his fans and his hometown. Hies final encore song was none other that ‘Born In the U.S.A.’ originated by Bruce “The Boss” Springsteen. This was a patriotic ending to a great show and I encourage each and everyone of us to make it to one of his shows in the future.