Anna Malmros

Ultralow-Power Cryogenic InP HEMT With Minimum Noise Temperature of 1 K at 6 GHz

We present in this letter an InGaAs/InAlAs/InP high-electron-mobility transistor (InP HEMT) with record noise temperature at very low dc power dissipation. By minimizing parasitic contact and sheet resistances and the gate current, a 130-nm-gate-length InP HEMT was optimized for cryogenic low-noise operation. When integrated in a 4- to 8-GHz three-stage hybrid low-noise amplifier operating at 10 K, a noise temperature of 1.2 K ± 1.3 K at 5.2 GHz was measured. The gain of the amplifier across the entire band was 44 dB, consuming only 4.2 mW of dc power. The extracted minimum noise temperature of the InP HEMT was 1 K at 6 GHz.

Electrical properties, microstructure, and thermal stability of Ta-based ohmic contacts annealed at low temperature for GaN HEMTs

Ta-based ohmic contacts to gallium nitride high electron mobility transistor (GaN HEMT) epitaxial structures were investigated. Two metallization schemes were considered: Ta/Al/Ni(Ta)/Au and Ta/Al/Ta. The latter was superior in terms of lower contact resistance (R-c) and wider process window. The metallizations were applied to two different heterostructures (GaN/Al0.14Ga0.86N/GaN and Al0.25Ga0.75N/GaN). The lowest measured R-c was 0.06 and 0.28 Omega mm, respectively. The main advantage of the Ta-based ohmic contacts over conventional Ti-based contacts was the low anneal temperature. The optimum temperature of annealing was found to be 550-575 degrees C. From optical and scanning electron microscopy, it was clear that excellent surface morphology and edge acuity were obtained at these low temperatures. This facilitates lateral scaling of the GaN HEMT. TEM images were taken of the contact cross sections onto which EDX measurements were performed. The aim was to investigate the microstructure and the contact mechanism. Storage tests at 300 degrees C for more than 400 h in air ambient showed no deterioration of R-c.

Evaluation of Thermal Versus Plasma-Assisted ALD Al 2 O 3 as Passivation for InAlN/AlN/GaN HEMTs

Al2O3 films deposited by thermal and plasma-assisted atomic layer deposition (ALD) were evaluated as passivation layers for InAlN/AlN/GaN HEMTs. As a reference, a comparison was made with the more conventional plasma enhanced chemical vapor deposition deposited SiNx passivation. The difference in sheet charge density, threshold voltage, fT and fmax was moderate for the three samples. The gate leakage current differed by several orders of magnitude, in favor of Al2O3 passivation, regardless of the deposition method. Severe current slump was measured for the HEMT passivated by thermal ALD, whereas near-dispersion free operation was observed for the HEMT passivated by plasma-assisted ALD. This had a direct impact on the microwave output power. Large-signal measurements at 3 GHz revealed that HEMTs with Al2O3 passivation exhibited 77% higher output power using plasma-assisted ALD compared with thermal ALD.

TiN thin film resistors for monolithic microwave integrated circuits

Titanium nitride (TiN) thin film resistors (TFRs) have been fabricated by reactive sputter deposition. The TFRs were characterized in terms of composition, thickness, and resistance. Furthermore, a first assessment of the resistor reliability was made by measurements of the resistivity (rho) versus temperature, electrical stress, long-term stability, and thermal infrared measurements. TiN layers with thicknesses up to 3560 angstrom, corresponding to a sheet resistance (R-s) of 10 Omega/square, were successfully deposited without any signs of stress in the films. The critical dissipated power (P-c) showed a correlation with the resistor footprint-area indicating that Joule-heating was the main cause of failure. This was partly substantiated by the thermal infrared measurements.

Low resistive Au-free, Ta-based, recessed ohmic contacts to InAlN/AlN/GaN heterostructures

The formation of recess etched Au-free ohmic contacts to an InAlN/AlN/GaN heterostructure is investigated. A Ta/Al/Ta metal stack is used to produce contacts with contact resistance (R-c) as low as 0.14 Omega mm. It is found that R-c decreases with increasing recess depth until the InAlN barrier is completely removed. For even deeper recesses R-c remains low but requires annealing at higher temperatures for contact formation. The lowest R-c is found for contacts where the recess etch has stopped just above the 2D electron gas channel. At this depth the contacts are also found to be less sensitive to other process parameters, such as anneal duration and temperature. An optimum bottom Ta layer thickness of 5-10 nm is found. Two reliability experiments preliminary confirm the stability of the recessed contacts.

Cryogenic 0.5–13 GHz low noise amplifier with 3 K mid-band noise temperature

A 0.5–13 GHz cryogenic MMIC low-noise amplifier (LNA) was designed and fabricated using a 130 nm InP HEMT process. A packaged LNA has been measured at both 300 K and 15 K. At 300 K the measured minimum noise temperature was 48 K at 7 GHz. At 15 K the measured minimum noise temperature was 3 K at 7 GHz and below 7 K within the entire 0.5–13 GHz band. The gain was between 34 dB and 40 dB at 300 K and between 38 dB and 44 dB at 4 K.

InGaAs-InAlAs-InP HEMT technology for ultra-high frequency and ultra-low noise performance

InGaAs-InAlAs-InP HEMT is facing competition from the emerging MHEMT technology. Nonetheless, for top-performing applications requiring high gain and low noise, InP HEMT is still the preferred choice. We here present results from InP HEMT development for sub-100 nm gate length designs yielding f/sub max/ above 400 GHz and ultra-low noise hybrid amplifiers with a minimum noise temperature of 1.1 K when operated under cryogenic conditions.

Low-Pressure-Chemical-Vapor-Deposition SiNx passivated AlGaN/GaN HEMTs for power amplifier application

A Low-Pressure-Chemical-Vapor-Deposition (LPCVD) bilayer SiNx passivation scheme has been investigated and developed, which effectively suppress the current collapse in AlGaN/GaN HEMTs. Low current slump is very helpful for microwave power amplifier application. Compared to in-situ SiNx passivations by metal-organic-chemical-vapor-deposition (MOCVD) and ex-situ SiNx passivations by plasma-enhanced-chemical-vapor-deposition (PECVD), the LPCVD SiNx exhibits the quickest recovery time from double-sweep IV curves. From pulsed IV and load-pull measurements, LPCVD SiNx is also confirmed to deliver superior large signal performance. The bilayer LPCVD SiNx passivated device shows negligible current slump (<;6%). These characteristics are directly reflected in the large signal operation, where HEMTs with bilayer LPCVD SiNx have highest output power (2.9 W/mm at 3 GHz).

A comparison of cryogenically cooled pseudomorphic and lattice matched InP HEMTs: Implementation in an ultra-low noise amplifier

A comparison between lattice matched (lm) and pseudomorphic HEMTs (pHEMTs) aimed for cryogenically cooled low-noise amplifiers (LNAs) has been performed. The DC and RF performance of the HEMTs at room temperature (RT) has been investigated. The devices have been tested in a hybrid 4 - 8 GHz LNA. While the gain and noise were superior for the pHEMT compared with the lm HEMT at RT, the noise performance was slightly inferior for the pHEMT when cooled to 20 K. The gain was still higher for the pHEMT at 20 K.