STI: Improving the Quality of Wireless®

What are superconductors?
When cooled to extremely low temperatures, certain materials experience zero electrical resistance at DC. They conduct current with no heat loss and are called superconductors. Zero electrical resistance logically provides better circuit performance for electronic components. In 1986, a new class of materials called high-temperature superconductors (HTS) was discovered that made the necessary cooling more cost-effective.

Superconductors have many different applications, ranging from levitating trains to ultra-efficient power lines. Superconductor Technologies Inc. (STI) has been developing high-quality superconducting materials and systems since 1987, focusing on the radio frequency segment of the wireless communications market with the thin-film microelectronics in its SuperLink® systems.

What are high-temperature superconductors (HTS)?
HTS material was discovered in late 1986 when Müller and Bednorz of IBM's Zurich Lab announced a superconducting oxide at 30 Kelvin (K). In 1987, Paul Chu of the University of Houston announced the discovery of a compound, Yttrium Barium Copper Oxide (YBCO), which became superconducting at 90 K. The next months saw a race for even higher temperatures that produced bismuth compounds (BSCCO) superconductive up to 110K and thallium compounds (TBCCO) superconductive up to 127K.

Does STI offer thin-film and/or thick-film superconductors?
STI focuses on thin-film rather than thick-film superconductors due to their substantial advantages in size, cost and performance. Thin films offer lower loss and up to 10,000 times higher microwave power handling than thick films.

STI's thin-film microelectronics address two critical needs in wireless communications: reducing signal interference and increasing base station sensitivity. Providing the industry with solutions to these critical issues has positioned Superconductor Technologies Inc. as the global leader in developing, manufacturing, and marketing superconducting products for wireless networks.

What are 1G, 2G, 2.5 G and 3G?
1G, or First Generation cellular systems, refers to networks which use an Analog air-interface to communicate between mobile devices and base stations. An example of this is the Analog AMPS (Advanced Mobile Phone System) systems deployed in the United States. Applications are generally limited largely to standard cellular telephone use.

2G, or Second Generation cellular systems, include TDMA (IS-136), CDMA (IS-95), and GSM air interfaces. These standards use a digital air interface to communicate between mobile devices and base stations. Initial applications were to provide basic cell phone functionality. However, additional features such as Caller-ID, voice mail , 1-way & 2-way SMS (Short Messaging Service), and low speed data port interconnection were subsequently added.

2.5G are enhanced 2G systems that are primarily aimed at supporting packet data, and a higher peak data rate, while still maintaining backwards compatibility to the parent 2G systems. GSM/GPRS is an example of a 2.5G system. There are some air interfaces, such as CDMA 2000 (1xRTT) and 1xEV, which tend to blur the line between 2.5G and 3G, since they provide peak data rate and packet transmission similar to 3G systems, but usually don't provide the voice capacity and/or have some backwards compatibility with an existing 2G standard.

3G, or Third Generation cellular systems, are similar to 2G systems in that they also employ a digital air interface between the handset and the base station. The primary differences are the peak data rates, the way data is delivered, and the number of simultaneous users that can be supported. While 2G systems were primarily designed to carry low bit rate conversations, 3G systems are designed to handle high data rates. Packet transport, as opposed to circuit-switched transport, is the primary method for moving data. In addition, the high channel bandwidth could be exploited to support more simultaneous voice and data calls (i.e. more capacity). Air interfaces such as WCDMA are considered 3G systems.

What is cryogenics?
Cryogenics is the study and use of materials at extremely low temperatures. The National Bureau of Standards suggests that the term cryogenics be applied to all temperatures below minus 150 degrees Celsius (-238°Fahrenheit or 123 Kelvin).

Cryogenic temperatures can be reached using a specially designed refrigerator, referred to as a cryocooler, or by submersing the device to be cooled in a fluid that boils at a low temperature. Liquids that are commonly used to achieve cryogenic temperature are Nitrogen, which boils at 77K, (-321°F, -196°C), and Helium, which boils at 4K, (-452°F or -269°C).

Cryocoolers achieve their cooling capability by either controlled evaporation of volatile liquids (using the heat of vaporization as the means to cool), by controlled expansion of gasses confined initially at high pressure (such as 150 to 200 atmospheres), or by acting as a heat-pump by alternatively expanding a gas near the area to be cooled (absorbing heat by the so-called heat of expansion), then compressing at another location (removing the heat by the heat of compression) in a closed-cycle. STI uses a closed-cycle cryocooler based upon the so-called Stirling cycle, which provides the highest efficiency, smallest size & weight of all known cryocooler cycles.

How does STI make its thin-film microelectronics, or microchips?
STI focuses on thin-film rather than thick-film superconductors due to their substantial advantages in size, cost and performance. Thin films offer lower loss and dramatically higher microwave power handling than thick films. The microwave current handling of thin films is up to 10,000 times higher than thick films. Several steps are involved in creating STI's thin-film microchips:

First, a nucleation layer is grown on a single crystal magnesium oxide substrate (the microchip wafer) by laser ablation. A pulsed ultraviolet laser is used to remove (ablate) material from a ceramic oxide target and deposit it on to the substrate in a controlled manner to allow thin-film crystalline growth.
Next, a 1 micron (0.00004") thick layer of the thallium-based superconducting compound is deposited, also by laser ablation.
The third step involves heating the film above its melting point in a controlled oxygen and thallium atmosphere. When cooled, a superconducting Tl 2 Ba 2 CaCu 2 O x single-crystal structure is formed. This crystallization process is sensitive to the substrate and nucleation materials used.

Last, the film undergoes several standard semiconductor photolithographic and fabrication steps, which result in a superconducting filter microchip.

(Back to top)

Feb	MAR	May
	25
2007	2008	2009