SMD - Technology

Vacuum nanoelectronics (VNE) uses IC processing technology to make vacuum devices with the size, cost and weight savings of solid state electronics. The difference between VNE and solid-state is ballistic transport: while electrons flow through silicon and other media, they shoot across a vacuum gap with an applied field under what can be very high voltages. This phenomenon is called field emission and the emitters are a type of “cold cathode”. See below for more on vacuum nanoelectronics.

Stellar Micro Devices and its people have achieved a number of firsts in vacuumnanoelectronics and vacuum micro-systems, which give SMD unique advantages in the applications shown below.

There are many potential applications of vacuum nanoelectronics and vacuum micro-systems. After analyzing dozens of them for feasibility and market potential, SMD has chosen to concentrate its effort into three primary areas: cold cathode devices, panels using cold cathode arrays, and vacuum micro-packages for MEMS and cold cathode devices. SMD is developing each area to be a separate product company.

Field emission cold cathodes turn on and off instantly, require no heater, occupy little space, can operate at high voltages, and are capable of very high speeds, both individually and in microwave or millimeter wave device configurations. They have achieved the highest current densities of any type of cathode. They can be made on wafers like semiconductor devices and can be integrated into circuits. They are essentially invulnerable to radiation and other events that can destroy solid state devices. SMD’s edge emitter devices also produce a natural sheet beam of electrons, a useful feature for many applications. Depending on the configuration, they can be used as ion sources and in a variety of scientific instruments. They can function as diodes, or be gated as “transistors” or tetrodes using Schottky, vacuum or optical gates. Made of or with photosensitive materials, they can produce highly efficient photodetectors in the IR, visible, UV, X-ray and higher bands. SMD has worked on several applications.

Individual Cathodes: SMD has developed very high current density vacuum-gated emitters for a client using an electron beam in an optical device. These cathodes are made of a proprietary carbon structure which has all the advantages of carbon nanotubes, but are easier to make and operate with a gate. Only SMD has this technology. SMD is also working with the Center for Space Sciences at the University of Texas at Dallas to develop ultra-rugged cold cathodes of carbides and nitrides for use with instruments operating in the corrosive environment of low earth orbit. SMD has made cathodes from more different materials than any other company and can provide the right cathode for the application to customers needing a vacuum electron source.

Vacuum Field Emission Amplifiers: SMD has made prototypes of “vacuum field emission transistors,” or VFETs, in projects for amplifiers in the X and Ka bands. VFETs are only slightly larger than solid sate amplifiers but operate at much higher voltages and potentially higher power levels than the GaAs or GaN FETs they resemble, and without their thermal limitations, since power is dissipated at the anode. VFETS have potential applications as base station amplifiers and in space communication systems.

Microwave and Terahertz Sources: Vacuum tube oscillators and amplifiers are widely used at very high frequencies for higher power levels than are possible with solid state or optical solutions. SMD recently began work with Boise State University on a “micro vacuum backward wave oscillator” as a tunable, lockable source in the Terahertz (0.1 to 1THz) region. The MBWO will incorporate a number of SMD innovations and can be used in molecular spectroscopy and terahertz imaging, a wide open field with the potential to revolutionize medical and security imaging. SMD has designed other Terahertz sources based on the Smith-Purcell and Gunn diode concepts.

Cold cathodes can be made into arrays of hundreds to millions of individual electron sources using process techniques developed for the semiconductor IC industry. SMD has equipment in house that can be used to make cold cathode arrays on glass or other panels up to 20 inches square, and larger panels can be made with new equipment. These panels can be used with phosphor plates for lighting, display or UV products, or they can be used with other targets to generate X-rays or deep UV. The emitter arrays can be turned on all at once, or individual cathodes can be addressed for small pixels of radiation. SMD got its start developing field emission displays (FEDs), but sees much better profit potential in radiation sources made using similar cathode arrays.

Field Emission Display. SMD has patents and prototypes for field emission displays. These include the electrical arrays for a 5-inch VGA display

Stacked Emissive 3D Display. SMD has developed prototypes of a 3D display using cold cathode arrays, and has designed other versions using other display technologies. 3D is the next frontier in display technology. SMD’s SEE3D display offers the accommodation, convergence, depth and binocular disparity features needed for true 3D for multiple viewers, without the glasses, head tracking or headaches that limit other approaches. SEE3D has potential in the medical imaging, home television, game and visualization markets.

All of SMD’s vacuum nanoelectronics devices and panels require a vacuum-tight package, so SMD has built considerable know-how in this area. The MEMS market, however, stands in greatest need of new packaging solutions, with many MEMS developers unable to find one that can satisfy requirements for low temperature sealing (to avoid damaging the devices), hermeticity and reasonable cost. SMD has developed a room temperature hermetic sealing process called compression bonded hermetic packaging (CBHP) which can meet these needs and demonstrated it on prototype packages. CBHP is suitable for a very wide range of single device packages made with metal, ceramic, glass and silicon. A future version using nano-scale materials will enable wafer-scale packaging on silicon.

SMD has three issued U.S. patents, other U.S. patents pending, a large number of disclosures, and several foreign patents.

5,965,971         Edge Emitter Display Device (Karpov)
6,023,126         Edge Emitter with Secondary Emission Display (Karpov)
6,607,930         Method of Fabricating a Field Emission Device with a Lateral Thin-Film Edge Emitter (Karpov, Eaton)
7,358,106         Hermetic MEMS Package and Method of Manufacture” (Potter)
20050263878   Cold Weld Hermetic MEMS Package and Method of Manufacture (Potter)
20070189459   Compact Radiation Source (Eaton, Karpov)

The theory behind field emission was developed by Fowler and Nordheim in 1928. Vacuum microelectronics was supported by the military during the Cold War for high power devices that could withstand radiation. Commercial development picked up in 1985, when the French research institute LETI made the first prototype FED using microtip cathodes. The VNE community continues to make advances in theory, characterization and many applications. Research papers on VNE are published in the Journal of Vacuum Science and Technology, B www.ojps.aip.org/jvstb.

The first International Vacuum Microelectronics (now Nanoelectronics) Conference was organized in 1988 by Dr. Kenneth Shoulders, Dr. Carl (Capp) Spindt of SRI and the late Dr. Henry Gray of the U.S. Naval Research Laboratory under the aegis of the IEEE Electron Devices Society. Sponsorship of the IVNC rotates between the U.S., Asia and Europe.