  X-ray hybrid CMOS detectors (HCDs) are a promising candidate for future x-ray
missions requiring high throughput and fine angular resolution along with large
field-of-view, such as the high-definition x-ray imager (HDXI) instrument on
the Lynx x-ray surveyor mission concept. These devices offer fast readout
capability, low power consumption, and radiation hardness while maintaining
high detection efficiency from 0.2 to 10 keV. In addition, x-ray hybrid CMOS
sensors may be fabricated with small pixel sizes to accommodate high-resolution
optics and have shown great improvements in recent years in noise and spectral
resolution performance. In particular, 12.5-{\mu}m pitch prototype devices that
include in-pixel correlated double sampling capability and crosstalk
eliminating capacitive transimpedance amplifiers, have been fabricated and
tested. These detectors have achieved read noise as low as 5.4 e-, and we
measure the best energy resolution to be 148 eV (2.5%) at 5.9 keV and 78 eV
(14.9%) at 0.53 keV. We will describe the characterization of these prototype
small-pixel x-ray HCDs, and we will discuss their applicability to the HDXI
instrument on Lynx.
