be solved through improved manufacturing processes, but only at the cost of lower yields, and consequently higher prices. Despite these issues, early BI sensors found uses in niche roles where their better low-light performance was important. Early uses included industrial sensors, security cameras, microscope cameras and astronomy systems. Other advantages of a BSI sensor include wider angular response (giving more flexibility for lens design) and possibly faster readout rates. Disadvantages include worse response uniformity. Industry observers noted that a back-illuminated sensor could theoretically cost less than a similar front-illuminated version. The ability to collect more light meant that a similarly sized sensor array could offer higher resolution without the drop in low-light performance otherwise associated with the megapixel (MP) race. Alternatively, the same resolution and low-light capability could be offered on a smaller chip, lowering costs. Key to attaining these advantages would be an improved process that addressed the yield problems, largely through improving the uniformity of an active layer on the front of the detectors. A major step in the adoption of BI sensors was made when OmniVision Technologies sampled their first sensors using the technique in 2007. These sensors, however, did not see widespread use due to their high costs. The first widely used BI sensor was the OmniVision OV8810, which was announced on 23 September 2008, and contained 8 megapixels which were 1.4 µm in size. The OV8810 was used in the HTC Droid Incredible and HTC EVO 4G, which were released in April and June 2009, respectively. In June 2009, OmniVision announced the 5MP OV5650, which had the best low-light sensitivity at 1300 mV/lux-sec and the lowest stack height at 6 mm in the industry. Apple selected the OV5650 to use in the back camera of the iPhone 4, which garnered good reviews for its low-light photos. Sony's work on new photodiode materials and processes allowed them to introduce their first consumer back-illuminated sensor as their CMOS-based "Exmor R" in August 2009. According to Sony, the new material offered +8 dB signaling and −2 dB noise. When combined with the new back-illuminated layout, the sensor improved low-light performance by as much as two times. The iPhone 4s employed an image sensor manufactured by Sony. In 2011, Sony implemented their Exmor R sensor in their flagship smartphone Sony Ericsson Xperia Arc. In January 2012, Sony developed the back-side illuminated sensor further with Stacked CMOS, where the supporting