Ba1−xSrxTiO3 (x =0.4) nanoparticles dispersion for 3D integration of decoupling capacitors on glass interposer

With the aim of scaling up and increasing the frequency of data processing within 3D integration, the placement of decoupling capacitors close to the chip is required in order to increase electrical performances of the module. Thin films deposition of materials with high permittivity (high k materials) (<; 100 nm) is critical for the fabrication of high density decoupling capacitor (>8 μF/cm
²
). Ba
_0.6
Sr
_0.4
TiO
₃
nanoparticles synthesized using supercritical fluid technique and presenting attractive properties, e.g. size ~15±2 nm, ε
_r
= 260 at 1 kHz for T = 300K, have been chosen to overcome technological limits for the realization of such high capacitance density thin films. In this paper, different approaches are proposed to disperse the nanoparticles, since their spontaneous agglomeration is critical. In order to reduce the size of these agglomerates (~500 nm), nanoparticles are dispersed in methanol or water. In both cases, the effects of the solution concentration and the ultrasonic homogenizer power on the dispersion of nanoparticles are examined. Ultrasonication is used to break the agglomerates. Dynamic light scattering is used to monitor the changes of agglomerates size. The process to take samples from solution was optimized. In the case of dispersion in methanol, the ultrasonication (power =100W - pulse 1s/3s) of concentrated solution (C ≥ 0.1 g/L) during 10 min, leads to agglomerates corresponding to 3-5 particles (60±10nm). In the second case, the measurement of Zeta potential gives access to the optimal pH conditions (pH <; 1.8 or > 9.7) for which the dispersion of Ba
_0.6
Sr
_0.4
TiO
₃
nanoparticles is stabilized.