Edwin L. Piner

12 W/mm AlGaN-GaN HFETs on silicon substrates

Al/sub 0.26/Ga/sub 0.74/N-GaN heterojunction field-effect transistors were grown by metal-organic chemical vapor deposition on high-resistivity 100-mm Si (111) substrates. Van der Pauw sheet resistance of the two-dimensional electron gas was 300 /spl Omega//square with a standard deviation of 10 /spl Omega//square. Maximum drain current density of /spl sim/1 A/mm was achieved with a three-terminal breakdown voltage of /spl sim/200 V. The cutoff frequency and maximum frequency of oscillation were 18 and 31 GHz, respectively, for 0.7-/spl mu/m gate-length devices. When biased at 50 V, a 2.14-GHz continuous wave power density of 12 W/mm was achieved with associated large-signal gain of 15.3 dB and a power-added efficiency of 52.7%. This is the highest power density ever reported from a GaN-based device grown on a silicon substrate, and is competitive with the best results obtained from conventional device designs on any substrate.

Enzymatic glucose detection using ZnO nanorods on the gate region of AlGaN∕GaN high electron mobility transistors

ZnO nanorod-gated AlGaN∕GaN high electron mobility transistors (HEMTs) are demonstrated for the detection of glucose. A ZnO nanorod array was selectively grown on the gate area using low temperature hydrothermal decomposition to immobilize glucose oxidase (GOx). The one-dimensional ZnO nanorods provide a large effective surface area with high surface-to-volume ratio and provide a favorable environment for the immobilization of GOx. The AlGaN∕GaN HEMT drain-source current showed a rapid response of less than 5s when target glucose in a buffer with a pH value of 7.4 was added to the GOx immobilized on the ZnO nanorod surface. We could detect a wide range of concentrations from 0.5nMto125μM. The sensor exhibited a linear range from 0.5nMto14.5μM and an experiment limit of detection of 0.5nM. This demonstrates the possibility of using AlGaN∕GaN HEMTs for noninvasive exhaled breath condensate based glucose detection of diabetic application.

Pressure-induced changes in the conductivity of AlGaN∕GaN high-electron mobility-transistor membranes

AlGaN∕GaN high-electron-mobility transistors (HEMTs) show a strong dependence of source∕drain current on the piezoelectric-polarization-induced two-dimensional electron gas. The spontaneous and piezoelectric-polarization-induced surface and interface charges can be used to develop very sensitive but robust sensors for the detection of pressure changes. The changes in the conductance of the channel of a AlGaN∕GaN high electron mobility transistor (HEMT) membrane structure fabricated on a Si substrate were measured during the application of both tensile and compressive strain through changes in the ambient pressure. The conductivity of the channel shows a linear change of −(+)6.4×10−2mS∕bar for application of compressive (tensile) strain. The AlGaN∕GaN HEMT membrane-based sensors appear to be promising for pressure sensing applications.

AlGaN/GaN HFETs fabricated on 100-mm GaN on silicon (1 1 1) substrates

Abstract The group III-nitride material system has been demonstrated by many groups to produce high performance, heterostructure field effect transistors (HFETs). AlGaN/GaN heterostructures yield high two-dimensional electron gas densities with high carrier mobilities and simultaneous high breakdown field. Devices based on this structure perform well at high power and at high frequency operating conditions. Most AlGaN/GaN HFETs to date have been produced on sapphire or silicon carbide substrates due to the limited availability of bulk GaN substrates. There are limitations in using these substrate materials in either thermal conductivity, cost or wafer diameter. The use of silicon substrates can overcome the issues of sapphire and SiC that limit manufacturability. In this work, results from HFETs fabricated on 100-mm silicon substrates using a proprietary MOCVD reactor design will be presented. The quality and uniformity of the GaN epitaxy, the microwave characterization of these devices at 2 GHz, and the thermal performance of large periphery devices on this material will be detailed. The electrical performance of these devices is found to be comparable to that of early devices on sapphire and SiC. The results will illustrate the viability of silicon as a low cost, manufacturable platform for AlGaN based devices from the standpoint of epitaxy, device performance, and thermal power handling.

Effect of Gate Leakage in the Subthreshold Characteristics of AlGaN/GaN HEMTs

This letter studies the effect of gate leakage on the subthreshold slope and ON/OFF current ratio of AlGaN/GaN high-electron mobility transistors (HEMTs). We found a strong correlation between the gate leakage current and the transistor subthreshold characteristics: the lower the gate leakage, the higher the ON/OFF ratio and the steeper the subthreshold slope. To improve the subthreshold characteristics in GaN HEMTs, the gate leakage current was reduced with an O2 plasma treatment prior to the gate metallization. The O2 plasma treatment effectively reduces the gate leakage current by more than four orders of magnitude, it increases the ON/OFF ratio to more than seven orders of magnitude and the improved AlGaN/GaN HEMT shows a nearly ideal subthreshold slope of 64 mV/dec.

A comparative study of surface passivation on AlGaN/GaN HEMTs

Abstract Using a Si 3 N 4 layer as passivation layer, effects of surface passivation on device performances have been investigated. After passivation, devices exhibited better pinch-off characteristics and lower gate leakage current. For a device with a gate-length of 0.25 μm, the I dss increased from 791 to 812.2 mA/mm and the peak extrinsic transconductance increased from 207.2 to 220.9 mS/mm. The f T and f MAX values decreased from 53 and 102.5 to 45.9 and 90.5 GHz, respectively, due to the increase of parasitic capacitances. Microwave noise measurements showed that devices exhibited 0.2–0.25 dB increase in minimum noise figure (NF min ) after passivation.

Electrical detection of deoxyribonucleic acid hybridization with AlGaN∕GaN high electron mobility transistors

Au-gated AlGaN∕GaN high electron mobility transistor (HEMT) structures were functionalized in the gate region with label-free 3′-thiol-modified oligonucleotides. This serves as a binding layer to the AlGaN surface for hybridization of matched target deoxyribonucleic acid (DNA). X-ray photoelectron spectroscopy shows the immobilization of thiol-modified DNA covalently bonded with gold on the gated region. Hybridization between probe DNA and matched or mismatched target DNA on the Au-gated HEMT was detected by electrical measurements. The HEMT drain-source current showed a clear decrease of 115μA as this matched target DNA was introduced to the probe DNA on the surface, showing the promise of the DNA sequence detection approach for biological sensing.

Prostate specific antigen detection using AlGaN∕GaN high electron mobility transistors

Antibody-functionalized Au-gated AlGaN∕GaN high electron mobility transistors (HEMTs) were used to detect prostate specific antigen (PSA). The PSA antibody was anchored to the gate area through the formation of carboxylate succinimdyl ester bonds with immobilized thioglycolic acid. The AlGaN∕GaN HEMT drain-source current showed a rapid response of less than 5s when target PSA in a buffer at clinical concentrations was added to the antibody-immobilized surface. The authors could detect a wide range of concentrations from 10pg∕mlto1μg∕ml. The lowest detectable concentration was two orders of magnitude lower than the cutoff value of PSA measurements for clinical detection of prostate cancer. These results clearly demonstrate the promise of portable electronic biological sensors based on AlGaN∕GaN HEMTs for PSA screening.

DC, RF, and microwave noise performance of AlGaN-GaN field effect transistors dependence of aluminum concentration

AlGaN-GaN heterostructures with different Al concentrations (20, 27, and 35%) were grown by metal-organic vapor phase epitaxy (MOVPE) on sapphire substrates. Ti-Al-Ti-Au ohmic contact optimization was investigated at different temperatures and annealing time. Heterojunction field effect transistors (HFET) with a gate length of 0.25 /spl mu/m were fabricated. Low contact resistances of 0.2, 0.26, and 0.33 /spl Omega//spl middot/mm were obtained for HFET device samples with Al concentrations of 20, 27, and 35%, respectively. For Al concentration of 20, 27, and 35%, the AlGaN-GaN devices exhibited extrinsic transconductances of 143, 152, and 210 mS/mm, I/sub dss/ of 398, 566, and 784 mA/mm, unity cutoff frequencies (f/sub T/) of 24.9, 34.6, and 50 GHz and maximum oscillation frequencies (f/sub MAX/) of 54.9, 61.8, and 100.9 GHz and minimum noise figures (F/sub min/) of 2.01, 1.47, and 1.02 dB at 12GHz, respectively. The calculated minimum noise figures have a good agreement with the measured values for all the devices with different Al mole fractions. The noise analysis shows that intrinsic noise of these AlGaN-GaN FETs plays a prominent part in the noise behavior because of improved device parasitics.

Fast electrical detection of Hg(II) ions with AlGaN∕GaN high electron mobility transistors

Bare Au gated and thioglycolic acid functionalized Au-gated AlGaN∕GaN high electron mobility transistors (HEMTs) were used to detect mercury (II) ions. Fast detection of less than 5s was achieved for thioglycolic acid functionalized sensors. This is the shortest response time ever reported for mercury detection. Thioglycolic acid functionalized Au-gated AlGaN∕GaN HEMT based sensors showed 2.5 times larger response than bare Au-gated based sensors. The sensors were able to detect mercury (II) ion concentration as low as 10−7M. The sensors showed an excellent sensing selectivity of more than 100 for detecting mercury ions over sodium or magnesium ions. The dimensions of the active area of the sensor and the entire sensor chip are 50×50μm2 and 1×5mm2, respectively. Therefore, portable, fast response, and wireless based heavy metal ion detectors can be realized with AlGaN∕GaN HEMT based sensors.