Plamen Kostov

Integrated phototransistors in a CMOS process for optoelectronic integrated circuits

This work presents integrated pnp phototransistors built in a 0.6 µm OPTO ASIC CMOS process using a low doped epi wafer as starting material. Several phototransistors with different designs of the base and emitter area were realized and characterized. For these novel photodetectors responsivities up to 65 A/W for DC light and up to 37.2 A/W for modulated light were achieved. Other transistors reach bandwidths up to 14 MHz. Due to the used standard silicon CMOS process low-cost integration is possible. Analog and digital circuitry can be implemented together with active optical detectors. This paves the way for high performance optical sensors and cost efficient SoC devices. Typical application examples include highly sensitive optical sensors, active pixel image sensors, light barriers and optical distance measurement sensors as well as 3D cameras.

Time-Of-Flight range finding sensor using an integrated PNP PIN Phototransistor in 180 nm CMOS

In this work we present the first approach of a Time-Of-Flight (TOF) sensor with an integrated bandwidth enhanced pnp phototransistor. The pixel reaches a fill factor of 67 %. A standard 180 nm CMOS process was used for implementing the TOF sensor together with the phototransistor. Both were combined to an optoelectronic integrated circuit. The power consumption of the sensor was 900 nW. Standard deviations of the measured distances well better than 5.1 cm were achieved for realistic optical powers in the range of nW. For the optimal working point of the phototransistor at around 100 nW a standard deviation of only 1.6 mm was measured.

High-speed PNP PIN phototransistors in a 0.18 μm CMOS process

In this work we present three speed optimized types of phototransistors built in a standard 180 nm CMOS technology without process modifications. An OPTO ASIC wafer consisting of a p⁺ substrate with a low doped p⁺ epitaxial layer on top of it is used for the implementation. The phototransistors were produced in 40×40 μm² and 100×100 μm² sizes. A gain in responsivity of more than 13 and bandwidths up to 50.7 MHz are achieved. As emitter followers, these phototransistors open the opportunity for application where high-speed photosensitive devices with inherent gain are needed. Possible applications are high speed opto-couplers, optical sensors, image sensors, etc.

Low frequency noise in CMOS PNP PIN phototransistors

Low frequency noise on six different types of CMOS PNP PIN phototransistors was investigated and is presented in this paper. The output noise spectral density is evaluated by a noise model for the investigated phototransistors. The current gain β and the most dominant shot noise terms including their values of each phototransistor are extracted. The presented phototransistors show a good noise performance.

Development and verification of a CMOS phototransistor noise model

In this paper a noise model for phototransistors is presented. Noise measurements and Gummel measurements on four different phototransistors were performed to verify the noise model. In addition, the output noise current density was modeled and compared with the measurements. A maximum difference of less than 12 % is noticed.

Electronics-Based 3D Sensors

The conventional photodiode, available in every CMOS process as a PN junction, can be enriched by smart electronics and therefore achieve interesting performance in the implementation of 3D Time-Of-Flight imagers. The high level of integration of deep submicron technologies allows the realization of 3D pixels with interesting features while keeping reasonable fill-factors.

Bandwidth and gain enhanced pnp phototransistors for VIS and NIR light IN 180 nm CMOS

Two phototransistor concepts with a size of 40×40 μm2 are presented. These devices were implemented in a 180 nm standard CMOS process without process modifications. The use of a special starting material with a low doped p- epitaxial layer on top of the high doped p+ substrate opens the possibility for achieving high bandwidths and responsivities even for deep penetrating light. Optical characterization of the devices was done at 410 nm, 675 nm and 850 nm. Bandwidths up to 67 MHz and responsivities up to 12.35 A/W were achieved. These devices are well suited for integrated optoelectronic circuits (OEICs).