This answer is based on the assumption that you already have an experience of research in your previous degree in a particular area of interest and you are willing to expand it through Ph.D. The research proposal should be based on this area of expertise only and the prescribed word limit should be followed. A research proposal for a Direct Ph.D. program at IIT Madras should include:
Let me explain this with the help of an example. You have a previous Master's degree in Biotechnology with work experience in cell culture. But you want to expand your research in cancer. Write a detailed idea of what, how, and why you are willing to conduct research in this field.
Your proposal will give a better picture of your research expertise and your level of knowledge to the panels and they will evaluate you based on your previous degree score, GATE score, written exam score, and viva performance apart from the proposal.
The research proposal primarily helps you in short-listing the professors under which you will work based on their area of research. You don’t need to be working on the topic you wanted and might have to work on the professor's research work.
Your proposal should portray your area of research work that is possible to be completed in 2-3 years.