We fabricated Bi2Sr2CaCu2O8+δ (Bi-2212) intrinsic Josephson junctions (IJJ) integrating of an oscillator and a detector by double side photolithography and material modification with a dilutehydrochloric acid solution (pH = 1.65) within a monolithic Bi-2212 crystal. The dilute hydrochloric solution modifies Bi-2212 to insulating BiOCl. Various lateral dimensions of the oscillator IJJ from 45 × 8 to 95 × 30 µm2 were formed; all of the detectors were about 15 × 10 to 15 × 30 µm2 in lateral dimensions. These stacks have 180–416 junctions. Zero voltage current for the detector stack was measured at 77 K while sweeping a bias voltage in the oscillator stack. The zero voltage current of the detector stack was strongly suppressed when a kink structure in the current–voltage curve of the oscillator stacks appeared. This indicates that the oscillator stack emits radiation at this voltage. From the Josephson voltage-frequency relation, it is found that the voltage corresponds to about 0.5–1 THz.
We fabricated Bi2Sr2CaCu2O8+δ (Bi-2212) intrinsic Josephson junctions (IJJ) integrating of an oscillator and a detector by double side photolithography and material modification with a dilutehydrochloric acid solution (pH = 1.65) within a monolithic Bi-2212 crystal. The dilute hydrochloric solution modifies Bi-2212 to insulating BiOCl. Various lateral dimensions of the oscillator IJJ from 45 × 8 to 95 × 30 µm2 were formed; all of the detectors were about 15 × 10 to 15 × 30 µm2 in lateral dimensions. These stacks have 180–416 junctions. Zero voltage current for the detector stack was measured at 77 K while sweeping a bias voltage in the oscillator stack. The zero voltage current of the detector stack was strongly suppressed when a kink structure in the current–voltage curve of the oscillator stacks appeared. This indicates that the oscillator stack emits radiation at this voltage. From the Josephson voltage-frequency relation, it is found that the voltage corresponds to about 0.5–1 THz.
Using a newly developed double-side fabrication method, an IJJ stack plus a bow-tie antenna and chokes were integrated in a slice 200 nm thick and singled out from inside a bulk Bi2Sr2CaCu2O8+x (BSCCO) single crystal. The junctions in the fabricated stack were very uniform, and the number of junctions involved was rather controllable. In addition to this method, which can be used to fabricate integrated circuits based on intrinsic Josephson junctions in high temperature (Tc) superconductors, also reported will be terahertz responses of IJJs, and the possible applications in quantum voltage standard, spectroscopy, and so on.
Using a double-sided fabrication method, we fabricated Bi2Sr2CaCu2O8(BSCCO) intrinsic Josephson junctions (IJJs) with a gold-BSCCO-gold structure. Coherent emission is observed at large dc input power, where a hot spot and “cold” part of the stack, coexist. The power, directly detected with a bolometer, is as high as 25 μW, implying the integrated power should be already in the order of sub-mW. We have successfully pumped a Nb-based Josephson junction and a grain boundary Josephson junction. Also with a wide tunable frequency range, BSCCO THz emitters will find themselves many practical applications, e.g., local oscillators of SIS, HEB, and Josephson mixers.
We report on Bi2Sr2CaCu2O8 (BSCCO) intrinsic Josephson junction stacks with improved cooling, allowing for a remarkable increase in emission frequency compared to the previous designs. We started with a BSCCO stack embedded between two gold layers. When mounted in the standard way to a single substrate, the stack emits in the range of 0.43–0.82 THz. We then glued a second, thermally anchored substrate onto the sample surface. The maximum voltage of this better cooled and dimension-unchanged sample was increased and, accordingly, both the emission frequencies and the tunable frequency range were significantly increased up to 1.05 THz and to 0.71 THz, respectively. This double sided cooling may also be useful for other “hot” devices, e.g., quantum cascade lasers.
The microwave distribution inside a rectangular stack (15 μm×0.72 μm×60 nm) of Bi2Sr2CaCu2O8+x intrinsic Josephson junctions (IJJs) was studied. The stack was microfabricated into a transmission-line geometry, with a-few-hundred-nm-thick Au layers deposited on the top and bottom of the stack. The microwave distribution was monitored by measuring the anomalous suppression of the tunneling critical current of the IJJs with varied microwave power at frequencies in the W band. This technique can provide valuable information on the microwave transmission modes inside the sandwiched stack of IJJs, which is utterly important for the high-frequency device applications using IJJs, such as fluxon-flow THz oscillators.
In a c-axis junction stack (10 μm×10 μm in a-b plane) patterned on a Bi2Sr2CaCu2O8+X single crystal, we performed harmonic mixings between a 100 GHz signal and up to the 98th harmonic of a local oscillator at about 1 GHz. The dependence of PIF on V, where PIF is the mixing output at the intermediate frequency and V is the dc voltage across the junction stack, was strongly affected by the local oscillator power levels. For low values of local oscillator power, the optimum operation point where PIF became maximum was around zero bias, and typical multi-branch structure of PIF vs V curves were observed. For high values of local oscillator power, the optimum operation point moved to the high-voltage region. In both cases, interesting oscillations occurred on the PIF vs V curves. Our experimental results led us to believe that intrinsic Josephson junctions can be good candidates for high frequency applications and the harmonic mixing may be a useful probe to investigate plasma phenomena in the layered superconductors.
With a 10 μm×10 μm mesa patterned on Bi2Sr2CaCu2O8 single crystals, we measure the current–voltage (I–V) curves of a stack of intrinsic Josephson junctions. Current steps are observed at an equal voltage spacing of 4 mV when the sample is subjected to microwave radiation at around 7 GHz. With increase of the microwave power, more steps occur while the spacing between neighboring steps does not seem to change. The magnitude of each step depends on the microwave power in an oscillating way. Tuning the microwave frequency causes such steps to occur over separate frequency ranges, and each range is quite narrow. A temperature rise from 4.2 to 14.3 K completely quenches the step structures. Possible explanations for the step structures, based on resonances excited by microwave or geometric resonances in the junction cavity, are discussed.