There are many short courses you can opt after your b.tech. 

Nanotechnology

Master of engineering on tool and design

Piping design in engineering course

Robotics course

Master of engineering in artificial intelligence and robotics

Master of engineering in automation and robotics 

Nanoengineering

Green nanotechnology

Wet nanotechnology

Etc

dear aspirant,

Mechatronics is a vast and inter-disciplinary field. At various universities including the IIT's it is offered at the PG level only.

If you have already undergone the course at UG level you can opt for a direct Ph.D or an Masters in the below:

1. Robotics

2. Automation

3. Control Systems

4. Hydraulic and Pneumatic Systems

5. Bio-Mechatronics, etc. are a few that come to mind.

Wish you all the best.