What are some differences between a Masters' Research Thesis versus a PhD Thesis for STEM fields? From program websites, I learned that a Masters thesis is not as "rigorous, broad, deep" as a PhD thesis, so I get the general idea that a Masters Research Thesis is "easier" than a PhD one. However, I find the description vague. In what specific ways are they different? How are the expectations different? Does a PhD thesis have to be "ground breaking", while a Masters one does not have to be? Can anyone who has written both types share their observations on the differences?
Master theses are short (duration-wise), PhD theses are long. How short and how long depends on details, but the relative difference is there regardless.
Master theses consist of one problem, while in STEM, PhD theses are often a collection of works which are not necessarily very closely related.
Both should contain original results. A 6-12 month master thesis which does not contain any original results has significant shortcomings.
From a supervisor's perspective: A master thesis which leads to one paper in a reputable journal is a good (top 1/3 or so) master thesis. A PhD thesis which only gives rise to one paper is a below average (lower 1/3) PhD thesis.