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A novel die sorter based on mechanical gripper was developed for picking and placing diced terahertz Schottky barrier diodes (SBD). The designing and working principle of die sorter are based on flexible hinge and linear-actuator. Dimensions of dies gripped by the sorter can be as small as 100 µm * 50 µm* 15 µm without damage to its air-bridge. For flipping upside down dies, the rotation motion was obtained by rotating linear actuator about its shaft. It is demonstrated that the placement accuracy of the sorter can achieve less than 9.5 µm and 3.0 µm in x-y direction respectively.

A 30 GHz monolithically integrated frequency multiplier based on the planar GaN Schottky barrier diode are successfully fabricated. The impact of material parameters and anode dimension on the frequency multiplier are investigated. The use of the monolithic integrated approach significantly improves the performance of the GaN frequency multiplier. The frequency multiplier gains a more than 3 dBm output power with frequency range from 21.5 to 39.5 GHz. The maximum output power is 9.68 dBm at 28.5 GHz with efficiency up to 16.1%. At the central frequency of 30 GHz, the output power is 9.64 dBm with 15.0% efficiency.

The fabrication and characteristics of balanced metal-semiconductor-metal (MSM) two-dimensional electron gas (2DEG) varactors based on AlGaN/GaN high electron mobility transistor (HEMT) for terahertz circuits were presented. The cathodes were designed to be strip-gates with submicron length of $\sim 450$ nm and manufactured by using electron beam lithography (EBL). The anodes lengths are ranging from $\sim 450$ nm to $\sim 2 \mu$m to study the influence of anode size on DC and high frequency characteristics. The DC and high frequency measurements were carried out, current-voltage and capacitance-voltage characteristics were investigated. As increasing the size of anode size to 2 $\mu $ m, the cutoff frequency of the MSM varactors was increasing as well. By matching the equivalent circuit at zero bias voltage with anode size of 2 $\mu$ m, the series resistance (R 0 ) of $\sim$ 32.43 $\Omega$, and the capacitance (C 0 ) of $\sim$ 5.09 fF were abstracted respectively, and the cutoff frequency of $\sim$ 964.6 GHz and the figure of merit (FOM) of 4.07 THz were obtained.

GaN Schottky barrier diodes have great potential for high power, high temperature and high frequency applications. We describe in this paper the design, fabrication and measurement of the GaN planar SBD with the air-birdge technology and electroplating technology for reducing the parasitic parameters. The typical On-wafer DC current-voltage and small-signal S-parameter measurements were characterized at room temperature, respectively. The impact of anode shape and dimension were investigated. The GaN planar SBD with $3\times 4\mu\mathrm{m}^{2}$ anode area had a cut-off frequency of 360 GHz and a breakdown voltage of -10 V.

The air-bridge interconnection is an extremely effective structure for improving the device performance in MMICs, but its application is limited by the complexity in fabrication and high temperature process required for baking photoresist. In this paper, we present a low temperature $( process for the fabrication of air-bridge in microwave devices. By choosing two types of suitable photoresists and optimizing the hard baking time of the sacrificial photoresist, we obtain high structural strength arched structure air-bridges with the entire process carried out at low temperature and complexity reduced. We have successfully fabricated four-finger HEMT devices.

In this paper we report on the fabrication and characterization of GaAs-based THz schottky barrier mixer diodes. Considering the analyzed results as well as fabrication cost and complexity, a group of trade-off parameters was determined. Electron-beam lithography and air-bridge technique have been used to obtain schottky diodes with a cut off frequency of 8.87 THz. Equivalent values of series resistance, ideal factor and junction capacitance of 10.2 (1) Ω, 1.14 (0.03) and 1.76(0.03) respectively have been measured for 0.7um diameter anode devices by DC and RF measurements. The schottky barrier diodes fabrication process is fully planar and very suitable for integration in THz frequency multiplier and mixer circuits. THz Schottky barrier diodes based on such technology with 2 μm diameter anodes have been tested at 1.6 THz in a sub-harmonic mixer.

In this letter, Ti/Pt/Au metal system has been investigated for the source/drain contact of MHEMT, the Ti/Pt/Au contact exhibits good ohmic contact characteristics with well thermal stability in the temperature range from 280 to 340°C. To further optimize the contact resistance, different metal deposition methods and contact layers are experimentally investigated. With sputtering Pd as an interlayer between Ti/Pt/Au and n+-InGaAs, the specific contact resistivity is further reduced to 3.51 × 10−5 Ω cm2. Meanwhile, by adopting this metal contact system, the MHEMT shows good DC and RF characteristics, including full channel current of 75 mA/mm, extrinsic maximum transconductance gm.max of 96 ms/mm, unity current gain cutoff frequency fT of 60 GHz and maximum frequency of oscillation fmax of 156 GHz. These good electrical characteristics demonstrate that this metal contact system is beneficial for the performance improvement of MHEMT. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:217–221, 2016

A planar Schottky barrier diode with the designed Schottky contact area of approximately 3 μm2 is developed on gallium arsenide (GaAs) material. The measurements of the developed planar Schottky barrier diode indicate that the zero-biased junction capacitance Cj0 is 11.0 fF, the parasitic series resistance RS is 3.0 Ω, and the cut off frequency fT is 4.8 THz. A monolithically integrated fourth subharmonic mixer with this diode operating at the radio frequency (RF) signal frequency of 0.34 THz with the chip area of 0.6 mm2 is implemented. The intermediate frequency (IF) bandwidth is from DC to 40 GHz. The local oscillator (LO) bandwidth is 37 GHz from 60 to 97 GHz. The RF bandwidth is determined by the bandwidth of the on chip antenna, which is 28 GHz from 322 to 350 GHz. The measurements of the mixer demonstrated a conversion loss of approximately 51 dB.

GaN Schottky barrier diodes(SBD) have shown great potential for high temperature, high power and high frequency applications. This paper presents the design, fabrication and measurement of the GaN planar SBD using the air-birdge Technology and electroplating Technology to reduce the parasitic parameters. An ohmic contact resistance of 0.15 Ω·mm was obtained with a Ti/Al/Ni/Au metal stack which is about 40% lower than a Ti/Al/Ti/Au metal stack. Also, we found the chemical treatment of the N+ GaN surfaces employing HCl+HF was better than BOE. Devices with various anode diameters(3–7μm) were fabricated on the same chip. The fabricated GaN SBD diodes were characterized by I-V and C-V measurements at DC. On-wafer small-signal S-parameter measurements were also performed up to 50 GHz. A cut-off frequency (f c ) of 627 GHz was achieved for GaN planar SBD with 7 μm anode diameter.

Resonant tunneling diodes (RTD) have the potential for compact and coherent terahertz (THz) sources operating at room temperature, but their low output power severely restricts their application in THz frequency range. In this paper, two methods are adopted to increase the peak current of RTD for enhancing its output power. First, different metal contact systems (including Pt/Ti/Pt/Au and AuGe/Ni/Au) for RTD contact are introduced, and a higher current of RTD with Pt/Ti/Pt/Au contact demonstrates the superior contact characteristic of Pt/Ti/Pt/Au contact system. Second, the double barrier structure (DBS) of RTD is well designed to further improve the characteristic of RTD, and a high peak current of 154 kA/cm2 is achieved at room temperature. The improved peak current is very beneficial for increasing the output power of RTD oscillator.