Multi-Functional Field Effect Switches Utilizing Anodized V/VO2/V Junctions

Vanadium oxides have a rich history because of the metal insulator transitions that several of the oxides and sub-oxides exhibit. In particular, VO2 has a metal–semiconductor transition just above room temperature in which this compound goes from a monoclinic crystal structure semiconductor below 340K to a rutile crystal structure metal above 345K with resistivity changes of more than four orders of magnitude. It has recently been discovered that there is also a current or charge-driven electronic transition that occurs in the semiconducting state that reduces the resistance by about an order of magnitude at current densities between 104 to 105 Amps/cm2 on time scales much less than 10 nanoseconds.

The current invention is an electric field effect switch utilizing anodized V/VO2/V junctions. Vanadium oxides whose properties can be dramatically altered with very small controlled changes of temperature, electric field or current are very desirable for a range of applications as switches, amplifiers or sensors. In particular, the abruptness of the VO2 phase transformation from its high temperature insulating tetragonal phase to its low temperature monoclinic metallic phase is accompanied by large changes (~103) in its electrical conductivity and infrared transmission characteristics, making it an excellent candidate for sensor and switching applications. Utilizing this metal insulator transition (MIT) in the VO¬2 phase as the basis for a switch is of particular interest as its transition temperature is around room temperature, ideal for practical applications. The stability of the phase on either side of the transition temperature makes for a robust and highly cyclable switch.

A processing method has been developed to fabricate lateral V/VO2/V junctions using anodization. Although the physical length scale of the junctions is ~ μm, these junctions show very strong non-linear tunnel-junction-like IV curves due to its nano-structure. The channel is “on” while VO2 is in the low resistance state (metallic) and is “off” while in the high resistance state (insulating). Because the resistivity of VO2 changes dramatically with small changes in temperature, current injection or electric field, we can control the state of the VO2 channel by changing these parameters, thereby turning on/off the current. Because it is a monolithic device, the fabrication will be much simpler compared to the conventional semiconductor transistor. It can be grown on SiO2/Si substrates which makes it fully integrable with conventional CMOS devices. Particular advantages of the current invention include:

1. Exceptional power handling and with much lower power dissipation: Resistivity of VO2 is very small in the metallic phase (much less than a semiconductor in the “on” state) allowing for higher currents. This may make it ideal for integrated power switch applications. In addition, compared to traditional semiconductor transistors, the contacts (source/drain) are all metals; therefore the power consumption can be much less due to the higher conductivity.

2. Fast and robust: Switching speeds much greater than 1 GHz and infinitely switchable are expected.

3. Flexible in control: The MIT of VO2 is determined by the phase compositions, doping and crystal quality. We can engineer thin films to function under a wide range of conditions.

4. Compatible: It can be fully integrated onto IC chips. 5. Cost efficient: It doesn’t require state-of-art lithographic facility, and the structure is much simpler compared to the conventional CMOS transistors.

Inventor(s): Wolf, Friedersdorf, Lu, Kirkwood, West

Type of Offer: Licensing



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