Figure 1: Details of the CBT device structure.
(a) Optical micrograph of the CBT with equivalent circuit diagram and schematic cross-section of the structure. Scale bar on the optical micrograph, 10 μm. The CBT is formed of 32 × 20 metallic islands of capacitance CΣ connected in an array by tunnel junctions of resistance RT, as shown in the circuit diagram. Connection to the array is made via on-chip RC filters comprising a meandering electrode sandwiched between large-area grounded metal films, separated by 250 nm SiOx. Each filter has a distributed resistance R≈500 Ω and capacitance C≈10 pF. The schematic cross-section shows one Al2O3 tunnel junction connecting two Al islands, with Au thermalization blocks on top of each. (b) Scanning electron microscopic (SEM) image showing Au thermalization blocks. Scale bar, 20 μm. (c) The sidewalls of four adjacent Au blocks. Scale bar, 4 μm. (d) One tunnel junction connecting two adjacent blocks. Scale bar, 1 μm.
