NHK and Tokyo University presented a nice alternative to TSV in stacked sensors on PRiME 2012 (Pasific Rim Meeting on Electrochemical and Solid-State Science) held in Honolulu, Hawaii on October 7-12, 2012:
"Development of novel MOSFET with front and back side electrodes for 3D-structured image sensors"
Masahide Goto, Kei Hagiwara, Yoshinori Iguchi, Hiroshi Ohtake, TakuyaSaraya, Hiroshi Toshiyoshi, and Toshiro Hiramoto
NHK Science and Technology Research Laboratories
The University of Tokyo
The proposal is quite simple (in a hindsight). In a multilayer image sensor structure one normally uses TSVs to transfer signals between the layers:
However, TSV size is quite big for the modern pixels of 1um size. Instead, the researchers propose a fully depleted SOI FET with front and back side contacts: