A device used to logically turn on a circuit with voltage being the input parameter
The device you're looking for is called a "voltage supervisor" or sometimes "reset controller". It monitors the supply voltage and asserts the reset input on the microcontroller until the voltage is within a particular acceptable range. Some also add a short delay after the voltage becomes acceptable before they release the reset signal

Many microcontrollers contain equivalent functionality built-in, where it's usually known as "brownout protection". Check whether yours supports this.

As yet another option, some voltage regulators include a "power good" output which may accomplish the same thing. This is more common on switching regulators but some LDOs have it too.