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for Visible Light
| Highly sensitive photo
transistors for visible light now are available in the high voltage
process ModuS U6 developed by PREMA Semiconductor. No additional
process layers are necessary for these transistors that can,
moderately priced, be integrated into mixed-signal ASICs. The photo transistors LS21 and LS31 offer a spectral sensitivity with a maximum in the visible range at about 610 nm. The LS21 is based on a super beta transistor with high gain that enables a high sensitivity even for weakest light signals. The spectral sensitivity at 610 nm is about 540 A/W, the LS31 based on a standard transistor offers a sensitivity of 70 A/W. Both photo transistors are very linear over a wide illumination range. 
Data
Sheet Photo Transistor
PDF
The light sensor SE15L consists of four super beta phototransistors LS21 combined to a differential stage. The transistors are placed in a quad split order to optimize the matching properties. Two transistors arranged in a diagonal are covered with metal. This differential stage amplifies the light current minus the dark current. An illuminance smaller than 1 Lux can be detected with the SE15L even at a chip temperature of 120°C. An ASIC has the advantage of optimizing the transistor matching whereas such a compensation of the dark current is difficult to achieve with discrete components. The photo transistors can be produced cost-effectively with the ModuS U6 process for custom specific analog ICs. The low number of defects even for a large light sensitive area guarantees a high wafer yield. A high sensitivity can be reached even with small sizes by using high gain super beta transistors. This combination of highly sensitive photo transistors and analog / digital analysing circuits offers a high grade of system integration and is well suited for a wide range of applications such as consumer electronics or automotive applications. |