Chipworks got a hold of Samsung S5K4E5 - a 1.4um pixel-based 5MP 1/4-inch mobile sensor. This is said to be Samsung's first BSI sensor with TSV technology. Samsung has indicated that it uses a lower-cost bulk silicon manufacturing process which they estimated to be 4x to 5x lower wafer cost compared with SOI.
The reverse engineering is ongoing. Meanwhile Chipworks released a photo of the sensor's backside: