## 2 Dark Current Noise Correction Method Based on Dark Pixels
### Preparation of the Dark Pixels QWIP  
This study used a GaAs/AlGaAs area array LWIR QWIP developed by the Shanghai Institute of Technology of the Chinese Academy of Sciences. The QWIP fabrication process used is as follows. Using a GaAs/AlGaAs material system [26], a 50-cycle quantum-well infrared detector structure was grown on a GaAs substrate using Molecular Beam Epitaxy (MBE) [27]. The grown material was tested in advance for optical parameters and single-component flow. The peak response was confirmed to be approximately 10.5 \(\upmu\)m. Next, a focal plane chip process was used; a SenTech ICPRIE SI500 (SenTech, Berlin, Germany) inductively-coupled plasma etching system grated the material. Ohmic electrodes were prepared via electron beam evaporation and alloyed using a rapid thermal annealing process to improve ohmic contact properties. Next, the reflective layer was prepared using ion-beam sputtering. Finally, the Inductively-Coupled Plasma (ICP) etching method was used to etch the pixels' isolation [28]. An Under-Bump Metallization (UBM) layer was grown and then chip cells were prepared in columns via a thermal evaporation of approximately 8 \(\upmu\)m [29]. After scribing, individual chips were interconnected with the readout circuit using hybrid inverted soldering; after interconnection, indium columns were reinforced with glue and then the GaAs substrate was thinned. As shown in Figure 2, it is a cross-sectional figure of the QWIP. The QWIP was equipped with a DI-type readout circuit [30], ISC9705 (with a response spectrum of 10-11 \(\upmu\)m), packaged inside a metal dewar with an integrated Stirling cooler RS058 (with a target cooling temperature of 50 K) developed by Wuhan Global Sensor Technology Company (Wuhan, China) [31]. After testing, the focal plane temperature control accuracy was within 0.3 K. Table 1 shows the QWIP's primary performance indicators.  
Figure 1: Schematic diagram of the dark current noise correction model.  
Sapphire was chosen as the patch material; its spectral properties dictate that it cuts off at a 6 um wavelength, eliminating the need for an optical film on the surface [32; 33]. Sapphire filters do not transmit LWIR radiation, are very chemically stable, have a Mohs hardness of 9, and are not easily deformed by vibration, making them suitable for designs oriented to complex scenario work. Therefore, a single-sided polished sapphire chip with a thickness of 430 um was selected. The schematic diagram of the QWIP used in this study is shown in Figure 3b; a sapphire patch of 30 pixel sized rows was laser cut and placed precisely on top of the target pixels. There was an error in the laser cutting process; 27 rows of dark pixels actually formed. The photoresist was dropped into both sides of the patch and the package was tested after complete solidification; the completed focal plane is shown in Figure 3a. The laser cutting edge shape was not regular and the influence of photoresist should be excluded. The actual use should be discarded as partial performance is not sufficient to meet the design requirements of the image data.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Detector Parameters** & **Parameter Values** \\ \hline Array size & 320 \(\times\) 256 \\ Pitch/um & 30 \\ \(f\)-number & 2.0 \\ Peak wavelength/um & 10.5 \\ Response bandwidth/um & \(\geq\)1.0 \\ Blind pixel rate & 0.75\% \\ Noise-Equivalent Temperature Difference/mK & 34.5 \\ Non-uniformity & 4.35\% \\ Cooling temperature/K & 50 \\ Frame rate/Hz & 20 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The QWIP’s primary parameters.  
Figure 3: Fabrication of QWIP with dark pixels; (**a**) QWIP with dark pixels; (**b**) design schematic of QWIP with dark pixels.  
Figure 2: The cross-sectional figure of the QWIP.