Pyroelectric detectors are widely used thermal infrared detectors due to their simple construction, robustness, and excellent performance. Most pyroelectric devices are based on monocrystalline lithium tantalate (LT) or pyroelectric lead zirconate titanate (PZT) thin films deposited on silicon (Si) substrate. In comparison, recently discovered pyroelectric doped hafnium oxide (HfO2) offers the possibility to manufacture completely CMOS-compatible devices on large silicon wafers.
Three-dimensional substrates with trench structures were applied for detectors to multiply the pyroelectric current responsivity of a thin, doped hafnium oxide layer deposited by atomic layer deposition. Micromechanical structuring of the 6” silicon wafers was used to improve the thermal conversion and effective plasmonic absorbers for the spectral range 3 - 5 μm.
An effective pyrocoefficient up to 1300 μC/m²/K was measured, depending on various dopants (Si, Al, La), layer thicknesses and polarization conditions. A high infrared light absorption > 80% of the plasmonic absorber in the relevant spectral range was determined using FTIR reflection measurements. The performance of the sensor element has been evaluated with a conventional analog transimpedance amplifier with a feedback resistance of 5 GΩ. A specific detectivity D* > 1 ∙ 107 cm√Hz/W (black body 1000 K, 3 - 5 μm) was measured for the frequency range 1 - 10 Hz.
Additionally, a new application-specific integrated circuit (ASIC) was used for the electrical signal conditioning to realize the first fully CMOS-compatible pyroelectric detector. This detector offers a flexible configuration, digital communication interface and achieves a similar signal-to-noise performance as the analog detectors.
