Single (111)-Wafer Fabrication of $100-\mu\mathrm{m}$ Scale Thermopile/Absorber Double-Deck Structure for High-Detectivity IR-Detection

This paper reports a
$100-\mu \mathrm{m}$
scale p
^+Si
/Au infrared (IR) thermopile detector with a novel thermopile/absorber double-deck structure, which is micromachined only from the front side of (111) silicon wafer for low-cost IC-foundry compatible manufacturing. The tiny-sized IR detector consists of six pairs of single-crystalline-silicon/ Au thermocouples that show significantly higher Seebeck coefficient and lower noise, compared with the traditional polysilicon/metal counterparts. In order to increase absorption of IR radiation, an umbrella-shaped S
i3
N
4
IR absorbing membrane is designed to replace the traditional plane IR absorbing film. The umbrella-shaped absorbing film is suspended above the thermopile layer to form a double-deck 3D-structure for increasing heat absorbing area. The novel structural configuration is realized to achieve high detectivity of the ultra-small sized (
$96\ \mu \mathrm{m}\times 106\ \mu\mathrm{m}$
) IR thermopile detector. The testing results demonstrate that the tiny-size IR thermopile detector achieves an ultra-high detectivity of
$1.01\times 10^{8}$
cm·Hz
^1/2
·W
⁻¹
and a fast response of 0.74ms.