  We demonstrated an ultra-broadband, polarization-insensitive and wide-angle
metamaterial absorber for terahertz (THz) frequencies using arrays of truncated
pyramid unit structure made of metal-dielectric multilayer composite. In our
design each sub-layer behaving as an effective waveguide is gradually modified
in their lateral width to realize a wideband response by effectively stitching
together the resonance bands of different waveguide modes. Experimentally, our
five layer sample with a total thickness 21um is capable of producing a large
absorptivity above 80% from 0.7 to 2.3 THz up to the maximum measurement angle
40{\deg}. The full absorption width at half maximum (FWHM) of our device is
around 127%, greater than those previously reported for THz frequencies. Our
absorber design has high practical feasibility and can be easily integrated
with the semiconductor technology to make high efficient THz-oriented devices.
