In FBK we develop different custom SiPM technologies. The so called NUV-SiPM are based on a p-on-n junction type, on n-type epi/substrate. This configuration enhances the photon detection efficiency (PDE) in the blue-wavelength region (PDE typically peaked at 400 nm), thanks to the electron-triggered avalanche when incoming photons are absorbed near the surface. The electron impact-ionization coefficient is higher than for holes and the trigger probability rises sharp already with few volts of excess bias (i.e. the difference between bias and breakdown voltage).

We recently developed a new high-density version of NUV-SiPM, called NUV-HD. Like RGB-HD technology, presented in [1], the devices feature a considerably high fill factor (FF) while reducing the correlated noise. This new NUV-HD technology combined all the benefits of the HD technology, i.e. high FF, increased photon detection efficiency, low correlated noise and high cell-density (thus high dynamic range), with the advantages of NUV approach (p-on-n junction) for light detection at short wavelength.

In the HD technology we use a small cell size (CS) and we implement trenches between cells. The reduction of cell size gives a lower gain of the cell, reducing both the afterpulsing and the amount of secondary-electrons, thus the optical crosstalk. Moreover, the trenches between cells provide optical isolation, further decreasing the crosstalk between cells. Thanks to this reduced correlated noise, it was possible to increase the FF to have a dead border region of about $1\div1.7~\mu m$.

We produced different SiPM prototypes with cell size of $15\times 15~\mu m^2, 20\times 20~\mu m^2, 25\times 25~\mu m^2, 30\times 30~\mu m^2$. The fill factor is 77% for the bigger cell and about 55% for the $15\times 15~\mu m^2$. Thanks to the technology development, the HD technology shows the same low dark count rate (DCR) of “standard” NUV-SiPM, i.e. in the order of 100 kcps (kilo counts per second), for 1 $mm^2$ device. The direct crosstalk probability is $\sim$30% for the bigger cell and only $\sim$7.5% for the SiPM with the smaller one, at $\sim$6 V of excess bias, while the afterpulsing and the delayed crosstalk is only $\sim$1%. The PDE of the 30-$\mu m$ cell SiPM is $\sim$40% already at low excess bias (as shown in the figure below), and it increases to $\sim$55% with 7 V. For the 15-$\mu m$ cell PDE is $\sim$33% with 7 V.

[1] C. Piemonte, A. Ferri, A. Gola, T. Pro, N. Serra, A. Tarolli, N. Zorzi, “Characterization of the First FBK High-Density Cell Silicon Photomultiplier Technology,” IEEE Trans. Electron Devices., vol. 60, no. 8, pp. 2567-2573, Aug. 2013.

Fondazione Bruno Kessler (FBK)

Fondazione Bruno Kessler (FBK)