5.1 Overview of this Chapter

The science return on any data can typically be enhanced if observers acquire a basic understanding of how the detectors operate, and of their individual characteristics and limitations. For the most demanding observations, such as imaging very faint or extremely bright sources, or for exposures using non-default parameters, an even deeper understanding of the detectors and their operation may be required. This chapter aims to provide both basic and in-depth information on the detectors used in both WFC3 channels. Sections 5.2-5.4 discuss the CCD detectors used in the UVIS channel, and Sections 5.5-5.7 discuss the infrared detector used in the IR channel.

Table 5.1 summarizes the basic characteristics of the flight CCD and IR detectors. For the CCDs, the information is either an average for the two chips, or the range of values for both of them. Results are based on ground measurements as well as on-orbit data acquired during 2009 and 2010 after WFC3 was installed in HST.

Table 5.1: WFC3 Detector Characteristics


UVIS Channel CCDs

IR Channel Detector


e2v CCD detectors.
Thinned, backside illuminated,
UV optimized,
multi-phase pinned,
buried/mini-channel, charge injection capability.

Teledyne HgCdTe infrared detector.
substrate removed,
on Si CMOS Hawaii-1R multiplexer.

Wavelength Range

200 to 1000 nm

800 to 1700 nm

Pixel Format

2 butted 2051 × 4096,
31-pixel gap (1.2")

1024 × 1024 (1014 × 1014 active)

Pixel Size

15 μm × 15 μm

18 μm × 18 μm

Plate Scale



Field of View on Sky

Rhomboidal, 162" × 162"

Rectangular, 136" × 123"

Quantum Efficiency

50–59% @ 250 nm1
68–69% @ 600 nm
47–52% @ 800 nm

77% @ 1000 nm
79% @ 1400 nm
79% @ 1650 nm

Dark Count

~9 e/hr/pixel (median, projected to May 2019)

0.048 e/s/pixel (median)

Readout Noise

3.1–3.2 e

20.2–21.4 e (pair of reads)
12.0 e (16-read linear fit)

Full Well2

63,000–72,000 e

77,900 e (mean saturation level)


1.55 e/DN

2.3 e/DN

ADC Maximum

65,535 DN

65,535 DN

Operating Temperature


145 Κ

1Quantum efficiency at 250 nm does not include multiple-electron events, which lead to larger apparent efficiency in e.g., Figure 5.2.
2The IR full well value is based on fully-integrated instrument ground testing. Other CCD and IR parameters are derived from on-orbit data.