Design aspects of Bi₂Sr₂CaCu₂O_8+δ THz sources: optimization of thermal and radiative properties

Abstract

Impedance matching and heat management are important factors influencing the performance of terahertz sources. In this work we analyze thermal and radiative properties of such devices based on mesa structures of a layered high-temperature superconductor Bi2Sr2CaCu2O8+δ. Two types of devices are considered containing either a conventional large single crystal or a whisker. We perform numerical simulations for various geometrical configurations and parameters and make a comparison with experimental data for the two types of devices. It is demonstrated that the structure and the geometry of both the superconductor and the electrodes play important roles. In crystal-based devices an overlap between the crystal and the electrode leads to appearance of a large parasitic capacitance, which shunts terahertz emission and prevents impedance matching with open space. The overlap is avoided in whisker-based devices. Furthermore, the whisker and the electrodes form a turnstile (crossed-dipole) antenna facilitating good impedance matching. This leads to more than an order of magnitude enhancement of the radiation power efficiency in whisker-based, compared to crystal-based, devices. These results are in good agreement with presented experimental data.

A distributed active patch antenna model of a Josephson oscillator

“…It is caused by the second term on the right-hand side, which enables nonlinear rectification of the Josephson current. The excess dc current is defined as (16) The oscillatory part is described by the equation (17) A comparison with Equation 1shows that this is the active TL equation in which the supercurrent wave, sin(kx + ωt), acts as a distributed (x,t)-dependent drive.…”

“…However, they emit very little power into free space [ 11 , 13 , 15 – 16 ]. The low radiation power efficiency, that is, the ratio of radiated to dissipated power, is commonly attributed to a large impedance mismatch between a Josephson junction (JJ) and free space [ 10 , 16 – 17 ]. But there is no consensus about the value of the junction impedance: Is it very small [ 16 ] or, in contrast, very large [ 10 ]?…”

Observation of collective excitation of surface plasmon resonances in large Josephson junction arrays

“…Terahertz sources of electromagnetic waves (EMWs) in the range of 0.1-10 THz are characterized by a low power efficiency [1][2][3][4][5][6]. Josephson junctions (JJs) can generate tunable terahertz radiation in a broad frequency range, from sub-terahertz in low-T c superconductors [7][8][9], to tens of terahertz in high-T c superconductors [10][11][12][13][14][15][16][17][18]. The performance of Josephson oscillators is limited by impedance mismatch [18,19] and self-heating [13,17,20,21].…”

“…Josephson junctions (JJs) can generate tunable terahertz radiation in a broad frequency range, from sub-terahertz in low-T c superconductors [7][8][9], to tens of terahertz in high-T c superconductors [10][11][12][13][14][15][16][17][18]. The performance of Josephson oscillators is limited by impedance mismatch [18,19] and self-heating [13,17,20,21]. Proper device engineering can obviate these obstacles and improve the performance [18].…”

“…The performance of Josephson oscillators is limited by impedance mismatch [ 18 – 19 ] and self-heating [ 13 , 17 , 20 – 21 ]. Proper device engineering can obviate these obstacles and improve the performance [ 18 ]. A single JJ is able to emit EMWs, but with a low power [ 22 ].…”