I've tried baking them at 450 degrees but they weren't crispy enough.
I don't think you need that high of a temperature. Bake them at 375 until they color evenly, then let cool completely. Are you using real Parmigiano Reggiano?
I use Ina's recipe and she adds a tablespoon of flour to the cheese.
350 degree oven, on parchment paper, 8-10 minutes, let rest 5 minutes. They crisp up as they cool
For simple frico you need nothing more than grated parmigiana and a non-stick skillet---ceramic if you have one. Heat the skillet on a gas burner and then add the cheese in small piles. Once it melts remove from heat.