  In this paper, the design trade-offs for the implementation of small
footprint thermal tuners on silicon nitride are presented, and explored through
measurements and supporting simulations of a photonic chip based on
Mach-Zehnder Interferometers. Firstly, the electrical properties of the tuners
are assessed, showing a compromise between compactness and deterioration.
Secondly, the different variables involved in the thermal efficiency, switching
power and heater dimensions, are analysed. Finally, with focus on exploring the
limits of this compact tuners with regards to on chip component density, the
thermal-cross talk is also investigated. Tuners with footprint of 270x5 {\mu}m
2 and switching power of 350 mW are reported, with thermal-cross talk, in terms
of induced phase change in adjacent devices of less than one order of magnitude
at distances over 20 {\mu}m. Paths for the improvement of thermal efficiency,
power consumption and resilience of the devices are also outlined
