Panasonic ZS40 has a
18.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor and features Venus Engine processor. On the other hand, Sony T90 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor .
Panasonic ZS40's sensor provides 6MP more than Sony T90's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the ZS40 and T90 sensor size comparison.
Panasonic ZS40 and Sony T90 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Sony T90 has 49% larger pixel area (2.34µm2 vs 1.56µm2) compared to Panasonic ZS40, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.