Research Terms
This gas sensor detects ammonia gas by utilizing a highly electron mobility transistor (HEMT), a device used to amplify or switch electronic signals and electrical power. Ammonia gas is used to reduce nitrogen oxides (NOx) through selective catalytic reduction (SCR) to prevent acid rain and smog formation. Various industries currently use ammonia gas to reduce emissions from boiler flue gases, refinery off-gas combustion, gas and diesel engines, gas turbines in the power industry and chemical process gas streams and more. However, monitoring and detecting ammonia gas is a required step in the process because high concentrations of ammonia in the environment can cause pollution and be toxic to terrestrial and aquatic organisms. Additionally, ammonia is flammable and can cause respiratory issues. In 2013, an ammonia fertilizer company exploded in Texas, killing 15 people and injuring more than 260 people.
Researchers at the University of Florida have developed a gas sensor that contains a highly sensitive and thermally stable GaN based HEMT with ZnO nanorods on the gate region of the sensor. This invention detects ammonia gas and other nitrogen compounds at low concentrations, preventing uncontrolled levels from harming the environment. Detection of ammonia at low concentrations is necessary for the refrigeration, agricultural, automotive, and chemical industries.
Gas sensor utilizes ZnO functionalized HEMT to increase detection sensitivity of ammonia gas
These gas sensors use GaN based HEMTs for low concentration ammonia detection. A layer of ZnO nanorods are used as functionalized gates to sense and measure ammonia concentrations. When exposed to ammonia, the conductivity of ZnO changes, causing the voltage readings from the sensor to change. The sensor works quickly and alerts its users when low levels of gas are present. The device can operate in harsh environments with high temperatures and receive no interference from other gases. This invention works both smoothly and efficiently, enabling its use in a variety of applications that require ammonia detection.
This chemical sensor is based on high electron mobility transistors and analyzes samples from exhaled breath to detect biological markers for breast cancer. The American Cancer Society projects more than 235,000 new diagnoses and 40,000 American deaths from breast cancer this year. Early detection -- when tumors are small and have not spread -- saves thousands of lives every year. The market for biosensors and chemical sensors has the highest rate of growth in the sensor industry and is expected to be worth $21 billion by 2016. Exhaled breath condensate is one of the most important bodily fluids that can be safely collected. Analyzing exhaled breath condensate provides valuable information about the metabolic state of the body and can help detect certain types of cancer, respiratory disease and liver and kidney function. Researchers at the University of Florida have developed a device that can quickly and accurately detect breast cancer in a saliva or exhaled breath condensate sample. The development of inexpensive sensing technologies that can detect and wirelessly transmit testing results could lead to significantly lower mortality rates and health care costs. The sensor also can be functionalized with different surface layers to detect a range of other materials such as heavy metal contamination in liquid samples.
Portable/handheld sensor for analysis of environment- and health-related samples such as breath, saliva, urine or blood
In this sensor, fluids adsorb onto AlGaN/GaN High Electron Mobility Transistors (HEMT), inducing charges from the polar molecules in the liquids bonded to the AlGaN/GaN surface. One end of the chemical of interest forms bonds with the Au and the other end bonds to cancer antibodies or forms chelates with ions of heavy metals, such as mercury, copper, and lead. The charges of the ions affect the gate potential of HEMTs, allowing the sensor to detect abnormal levels of chemicals in breath condensate or fluid, possibly identifying health problems.
This poly(methyl methacrylate) (PMMA)-encapsulated Schottky diode protects hydrogen sensors from humidity without affecting their ability to detect hydrogen. Hydrogen is a source of energy that powers different forms of transportation, buildings and industrial processes making it a valuable resource. However, hydrogen can become problematic because it is highly reactive, flammable, has low ignition energy, and has a high tendency to leak. Hence, it is crucial that efficient detection technologies are available to ensure the safe use of hydrogen. One of the biggest issues with GaN-based hydrogen sensors is their sensitivity to humidity. Exposure to ambient humidity significantly decreases the sensitivity because water molecules block the active sites of the sensor. Researchers at the University of Florida have enclosed hydrogen sensing diodes with PMMA to effectively mitigate the effects of water. This enables the sensors to work in a variety of humid environments and allows them to be modified to detect other gases.
Encapsulation of Pt-AlGaN/GaN Schottky diodes with water-blocking polymer layer provide a moisture barrier for gas sensors
This Schottky diode is completely enclosed in PMMA, which creates a barrier between the sensor and any source of water or moisture, preventing excess background noise and corrosion. The PMMA coating allows hydrogen molecules to diffuse through and reach the sensor while preventing water molecules from reaching the diode. By eliminating this problem, the hydrogen sensor has an increased range of environments in which it can be used and provides more precise measurement.
Devices fabricated that use this backside source field plate method operate at higher voltages and with better reliability due to the lower peak electric field and junction temperature. Field-effect transistors such as AlGaN/GaN high electron mobility transistors (HEMTs) have received increasing attention for high power and high frequency applications (i.e. military radar or satellite-based communications systems) due to their superior mobility and larger energy band gap as compared to Si-based power transistors. GaN epi-layers are usually grown on sapphire, silicon (Si), or silicon carbide (SiC) substrates. Of the three, silicon substrates are the most promising as a prime candidate for mass production of GaN, but the nucleation interfacial layer between GaN and Si causes inefficient heat dissipation. University of Florida researchers have overcome this deficiency by adding a Si-substrate via hole under the active area of the HEMT to decrease the junction temperature and dissipate the heat directly through the device’s active area. The modification reshapes the electric field in the channel, reduces the peak value on the drain side of the gate edge, and reduces the gate to drain capacitance. Depending on the requirement for specific applications, the backside field plate technique is applicable to forming gate or drain field plates as well with simple modifications.
Backside via hole technique for field effect transistors with improved heat dissipation and reliability
This semiconductor device and technique for a HEMT with improved heat dissipation includes a number of fabricated layers – the nucleation layer, the transition layer, a buffer, and a barrier -- built upon a substrate. Researchers etch the back side of the substrate to form a via hole through the substrate under the gate or active region of the HEMT through the layers and then fill the hole with metal. The metal-filled via hole decreases the junction temperature and dissipates the heat directly through the device’s active area.
These self-repairing semiconductor designs can be integrated into computer processors for radio communication in high temperature or high radiation environments. Worldwide sales of semiconductors in 2014 reached $335.8 billion, up 9.9 percent from 2013. Low-power satellites in outer space, cell phones and towers, or rugged military laptops use the toughest semiconductors available. They relay important information, such as GPS coordinates or digital messages. Because of hostile environmental conditions, quick temperature changes, and normal wear and tear, this expensive equipment needs regular replacement. Semiconductor manufacturers often use Gallium Nitride-based HEMT (High-electron-mobility transistor) semiconductors for radio frequency communications and direct current power. HEMTs are fast and resistant to noise, but HEMTs are not immune to all threats. Stresses such as moisture, localized heat, and voltage spikes might decrease processor performance, increase power consumption, and eventually lead to circuit failure. Thermal annealing -- applying a uniform heat source -- can undo some of that damage, but available methods are not feasible. Researchers at the University of Florida have developed an on-chip heater with a preset drain or gate current level. Now, whenever semiconductor chips conditions reach that preset level, an internal heater could turn on automatically and begin annealing the chips. After annealing, these chips could return to near-original electrical operating condition. No outside maintenance by the device owner would be needed.
High-performance, longer-lasting, self-repairing semiconductors for RF communication, AC to DC power conversion, and DC power amplification
The patent-pending semiconductor designs include an on-chip or on-substrate heater with a preset drain or gate current level. When the semiconductor conditions reach the preset level, the heater will automatically turn on and thermally anneal the chips. Research shows annealing will reverse or partially reverse effects such as forward and reverse bias current increase, the appearance of traps, sub-threshold swing increase, sub-threshold leakage increase, reverse bias gate leakage current increase, saturation drain current reduction, drain current on-off ratio reduction, gate current reduction, lower electromagnetic Schottky barriers, higher diode ideality factors, weaker small signal RF, and degradation at a metal-Aluminum Gallium Nitride interface. Overall, since a chip can regain lost performance even after multiple heat treatments, its life expectancy will increase.
