Fully 3-D Integrated Pixel Detectors for X-Rays

The vertically integrated photon imaging chip (VIPIC1) pixel detector is a stack consisting of a 500- $\mu \text{m}$ -thick silicon sensor, a two-tier 34- $\mu \text{m}$ -thick integrated circuit, and a host printed circuit board (PCB). The integrated circuit tiers were bonded using the direct bonding technology with copper, and each tier features 1- $\mu \text{m}$ -diameter through-silicon vias that were used for connections to the sensor on one side, and to the host PCB on the other side. The 80- $\mu \text{m}$ -pixel-pitch sensor was the direct bonding technology with nickel bonded to the integrated circuit. The stack was mounted on the board using Sn-Pb balls placed on a 320- $\mu \text{m}$ pitch, yielding an entirely wire-bond-less structure. The analog front-end features a pulse response peaking at below 250 ns, and the power consumption per pixel is 25 $\mu \text{W}$ . A successful completion of the 3-D integration is reported. In addition, all pixels in the matrix of $64\times 64$ pixels were responding on well-bonded devices. Correct operation of the sparsified readout, allowing a single 153-ns bunch timing resolution, was confirmed in the tests on a synchrotron beam of 10-keV X-rays. An equivalent noise charge of 36.2 $\text{e}^{-}$ rms and a conversion gain of 69.5 $\mu \text{V}/\text{e}^{-}$ with 2.6 $\text{e}^{-}$ rms and 2.7 $\mu \text{V}/\text{e}^{-}$ rms pixel-to-pixel variations, respectively, were measured.