Nanoscale Compositional and Strain Gradients Enable High‐Speed and Amplitude‐Resolved Pyroelectric Sensing

The frequency response of pyroelectric sensors is fundamentally governed by thermal time constant (τ th , determined by thermal mass and thermal conductance) and electrical impedance arising from film capacitance and readout circuit. Conventional bulk LiTaO 3 detectors are optimized for high responsivity at low modulation frequencies (0.1–10 Hz), possessing a large τ th that thermally averages rapid temperature oscillations at elevated modulation frequencies, limiting fidelity in resolving dynamic varying thermal signals. Here, compositional and strain gradients are introduced into 100‐nm‐thick relaxor‐ferroelectric films reducing τ th to ≈2 µs and producing built‐in potentials (≈1.45 V or 145 kV cm −1 ) that enhance the pyroelectric coefficient and suppress the dielectric constant. This enables complementary dual‐mode operation by enhancing current‐mode electrical responsivity and improving the voltage‐mode figure of merit – advantageous for superior temperature resolution (Δ T min ≈ 30 µK). The responsivity peak shifts to near 1 kHz (>2500‐times higher than conventional bulk sensors), with measurable responsivity extending to a carrier frequency of 100 kHz and amplitude‐resolved detection at modulation frequencies up to 15 kHz. These results establish nanoscale internal‐field engineering can reshape electro‐thermal trade‐off in pyroelectric thin films toward zero‐bias, high‐thermal‐sensitivity, and amplitude‐resolved thermal sensing across a wide frequency bandwidth.