A new microwave-compatible process for fabricating planar integrated resonant tunneling diodes (RTD's) is described. Successful fabrications of high-performance RTD's using AI,Ga, -,As/ In yGa, -,As/GaAs strained layers have been obtained. Peak-to-valley current ratios (PVR's) of 4.8:l with simultaneous peak current densities of 4 x lo4 A/cm* have been achieved at room temperature for diodes of area 9 pm2. Accurate measurements of reflection gain versus frequency between 1.5 and 26.5 GHz in the negative differential region indicate that the present technology is promising for millimeter-wave integrated circuits including self-oscillating mixers, frequency multipliers, and detectors.NTEGRATION of a resonant tunneling diode (RTD) in a I planar technology is attractive for several reasons. This is primarily because a planar structure is suitable for the realization of integrated microwave and millimeter-wave functions such as mixers, harmonic multipliers, and detectors. This is also because stable and high-frequency operation can be expected owing to the reduction of parasitic reactances. In addition, if the devices are fabricated with the necessary coplanar lines for microwave wafer probing, the overall reliability and accuracy of microwave measurements will be greatly improved because spurious selfoscillations will be eliminated in a large fraction of the negative differential resistance (NDR) bias range. Recently, there has been a proposal for a microwave-compatible process employing topside contacts and proton implantation resulting in isolated devices and transmission-line interconnections [ 11. At room temperature, the devices using AlAs-GaAs double-barrier heteroepitaxies exhibit a very high peak current density of about lo5 A/cm2 with peak-to-valley current ratios (PVR's) from 2 to 2.5.In this paper, we propose a new fabrication technology that can be used for the embedding of a RTD in a low-loss transmission-line environment. For the double-barrier resonant tunneling structure, Al,Ga, -,As/In,Ga, -,As/GaAs strained layers are grown on a semi-insulating (SI) substrate that serves as the IEEE Log Number 9142892. dielectric of transmission lines. A two-step mesa technology is used for the implementation of the transmission lines directly on the SI substrate. This avoids the proton isolation proposed in [l] that provides a nonconducting dielectric for transmission lines. In other respects passive elements such as tuning inductors could be incorporated onto the chip. We demonstrate that planar monolithic integrated RTD's with high current capability can be fabricated using this microwave-compatible technology and we report unique stable frequency variations of impedance of diodes biased in the negative resistance.The epitaxial material was grown by molecular beam epitaxy in a Varian GEN-I1 system. We start from a semi-insulating [loo], 2-in, substrate. The first layer grown was a highly doped layer (No = 2 x lo'* ~m -~) of GaAs of 1 pm followed by 50-nm-thick GaAs with a doping concentration of 2 x lo', ~m -~. S...
We report the realization of very small area resonant tunneling diodes (RTD's) for integrated microwave applications. Diodes with areas down to 3×3 μm2 were fabricated with the necessary coplanar lines for microwave wafer probing. Peak to valley ratios up to 3.5 with peak current densities ranging from 0.6 A/cm2 to 1.5 kA/cm2 have been achieved for Al0.4Ga0.6 As/GaAS double barrier heterostructures grown by MBE on Semi-Insulating substractes. Reflection gain versus frequency measurements in the 1.5-26.5 GHz range, at room temperature, were performed. The smaller devices exhibit a maximum cut off frequency for the negative differential resistance of 18 GHz. For high current versions, we expect significant increase in frequency limit
The microwave impedance of high current Al0.3 Ga0.7 As‐GaAs‐Al0.3 Ga0.7 As resonant tunneling diodes is measured from 0.1 to 12.1 GHz over a large bias range at 300 K. Using an equivalent circuit model, the bias dependence of intrinsic conductance and capacitance suffice to explain the pronounced variations of impedance.
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