Principal Investigators: DevSanRafael Quantum Labs & Joel Villarroel Published: April 2026 | Subject: DC-SQUID Fabrication • Bi-2212 Josephson Junctions
Abstract: Following the geometric optimization of the Bi-2212 lattice (Project SYNTHESIS), Project FACTORY executes the transition from atomic simulation to physical device integration. We detail the nanolithography pipeline utilized to carve High-Tc supercurrent circuits into bulk Bi-2212 crystals. By leveraging intrinsic c-axis Josephson coupling, we fabricated single DC-SQUIDs and massive multi-loop SQUID arrays. Electrical characterization demonstrates robust flux quantization up to 77K with sub-thermal noise floors for extreme metrological utility.
1.00 mA
ARRAY CRITICAL CURRENT (Ic) AT 77K
1. Intrinsic Josephson Junctions in Bi-2212
Unlike Niobium (Nb) or Aluminum (Al) based SQUIDs that require artificial oxidation layers (e.g., $AlOx$) to construct a Josephson Junction, the Bi-2212 layered structure provides natural weak-links. The superconducting $CuO_2$ planes are separated by semi-insulating $BiO$ layers.
By etching a mesa structure along the c-axis, we force the supercurrent to tunnel directly across these intrinsic junctions. This removes the need for highly variable artificial barriers and allows the device to operate comfortably at Liquid Nitrogen temperatures (77K) rather than relying on dilution refrigerators.
$I(\phi) = I_c \sin(\phi) + \frac{V}{R_n} + C \frac{dV}{dt}$
2. Nanolithography and Architecture
We deploy focused ion beam (FIB) milling on a macroscopic high-quality Bi-2212 crystal flake. The sequence carves out a topological network:
Single Loop SQUID: A primary ring with two parallel weak-links for ultra-sensitive single flux detection.
SQUID Arrays: A massively parallel network (up to 18 coupled loops). The periodic structure dramatically magnifies the Voltage-Flux modulation signal and boosts the critical current while maintaining the periodicity of a single SQUID.
3. Voltage-Flux Modulation & Noise Floor
The primary utility of the device is to act as a highly sensitive flux-to-voltage transducer. The V-I characteristic exhibits classic Shapiro-like resistively and capacitively shunted junction (RCSJ) behavior.
⚡ DC-SQUID Performance
10.5 Ω
Normal Resistance ($R_n$)
Periodic
Modulation Profile
The intrinsic 1/f noise spectrum approaches the thermodynamic floor limit rapidly at frequencies > 1 kHz, making the array an ideal candidate for readout mechanisms in High-Tc topological architectures.