If your goal is as you mention: "to study about how user interact with interface and also devices." Then I would recommend you to pursue studies on research methods, I would go for Social Sciences research methods made for psychologist, anthropologist, sociologist, etc. probably it would be out of your comfort zone since you would be subject of different teaching methods but since you already have a design background I would say having other point of view on how to see design research would be more enriching than pure design research.
I would also go to the Digital Humanities areas since they do research on diverse creative and experimental methodologies observe and interpret how human are interacting with technology.
For both I would recommend to look at the UK, places like UCL for Digital Humanities and Goldsmiths, LSE, etc. for Research Methods.
Maybe you could directly consider Design Research as a more straight and safe route, still if you have a bit of an oblique mindset as I do, you will value the richness that other disciplines can bring to your daily work.