Fig. 1. Effect of substrate interference on voltage response of detectors. (a) Schematic of Nb5N6 microbolometer with substrate cavity; (b) voltage response of the Nb5N6 microbolometer THz detector with frequency when the substrate cavity length is fixed. Dots represent relative voltage responses of the device while lines represent the simulation results of the square of electric field intensity at the device location with substrate thickness of L=300, 440, 580, and 720 μm[30]

Fig. 2. THz detector with tunable resonance frequency. (a) Schematic of the cavity setup; (b) continuous tuning of the microbolometer detector via different air gaps[31]

Fig. 3. Nb5N6 microbolometer quasi-optical receiver with series structure. (a) Package of the quasi-optical detector, with the microbolometer chip glued to the back side of the silicon lens; (b) Nb5N6 microbolometer consisting of three microbridges, three connected resonant dipole antennas, and pads. The inset top picture shows SEM micrograph of the Nb5N6 microbridge; (c) optical responsivity; (d) corresponding noise equivalent power[32]

Fig. 4. Optical microscope picture of fabricated five-staircase square silicon microlens array chip and SEM micrograph of an Nb5N6 microbolometer fabricated at the back center of the microlens[33]

Fig. 5. Nb5N6 microbolometer THz detector with a grating-coupled structure. (a) A cross-section SEM picture of the grating groove; (b) SEM image of Nb5N6 THz array detectors; (c) schematic of the reflective grating-coupled structure; (d) normalized voltage responsivity of the detector with the F-P cavity; (e) normalized voltage responsivity of the detector with the reflective grating-coupled structure[34]

Fig. 6. Chip structure of readout circuit. (a) Chip microphotograph of the 1×16 ROIC chip; (b) array ROIC diagram[35]

Fig. 7. Schematic of fabrication process of flip-chip technology. (a) UBM and SiO2 layers deposition; (b) solder bumps evaporation; (c) solder bumps refluxing; (d) detector and rewiring chip bonding[36]

Fig. 8. Array chip package diagrams. (a) Microscope image; (b) X-ray image; (c) SEM image of detector after flip-chip; (d) SEM image of a microbolometer with an air bridge[36]

Fig. 9. Comparison of optical response and electrical performance of devices. (a) Optical voltage responses under a 2-μm irradiation as a function of the bias current for samples A; (b) optical voltage responses under a 2-μm irradiation as a function of the bias current for sample B; (c) I-V curves of the detectors measured at room temperature. The insets show the inverse of the microbolometers' resistances (1/R) as a function of I2[37]