Willem Hoekstra

Silicon-based resonant-cavity-enchanced photodiode with a buried SiO2 reflector

We report on a silicon-based resonant cavity photodiode with a buried silicon dioxide layer as the bottom reflector. The buried oxide is created by using a separation by implantation of oxygen technique. The device shows large Fabry–Perot oscillations. Resonant peaks and antiresonant troughs are observed as a function of the wavelength, with a peak responsivity of about 50 mA/W at 650 and 709 nm. The leakage current density is 85 pA/mm2 at −5 V, and the average zero-bias capacitance is 12 pF/mm2. We also demonstrate that the buried oxide prevents carriers generated deep within the substrate from reaching the top contacts, thus removing any slow carrier diffusion tail from the impulse response.

Si/SiGe resonant-cavity photodiodes for optical storage applications

We report on a resonant cavity photodiode with a Si/SiGe Bragg mirror grown by low temperature chemical vapor deposition suitable for short wavelength detection around 600–700 nm. The presence of Fabry-Perot oscillations in the spectral response of the photodiode are indicative of its wavelength selectivity.

Memory read-out approach for a 0.5-μm CMOS image sensor

In image sensors with passive pixels the column capacitance is large compared to the capacitance of the pixel. The charge-to-voltage conversion occurs in the column amplifier relatively far from the pixel. This may result in a high sensitivity to interference, especially in cases other electronic circuitry is located on the same chip. Two types of CIF CMOS imagers are presented that use different read- out options to counter this effect. Both designs use differential read-out as DRAMs do. This means that the pixel is compared to a reference cell. The first type uses a reference cell on the same row; the second type utilizes a fully symmetrical way of read-out, similar to digital memories by having this reference on the same column. Furthermore, two other means of image quality improvement are applied. A boost circuit is sued to generate a negative voltage for driving the selecting transistor to insure that it is completely switched on during pixel reset. By this, threshold differences between pixels do not affect the reset voltage. The second is a well thought-out column amplifier that calibrates its offset before reading the pixel information.

Silicon-on-insulator resonant cavity photodiode without a slow carrier diffusion tail

We report on a novel silicon-based resonant cavity photodiode with a buried silicon dioxide layer as the bottom reflector. The buried oxide is created by using a separation by implantation of oxygen technique. The device shows large Fabry-Perot oscillations. Resonant peaks and anti-resonant troughs are observed as a function of the wavelength, with a peak responsivity of about 50 mA/W at 650 nm and 709 nm. The leakage current density is 85 pA/mm2 at -5 V, and the average zero-bias capacitance is 12 pF/mm2. We also demonstrate that the buried oxide prevents carriers generated deep within the substrate from reaching the top contacts, thus removing any slow carrier diffusion tail from the impulse response.