Design of a Movement Control Equipment for Crystal Growth by the Liquid Phase Epitaxy Technique

The design and construction of a device to perform and control the movements of the substrate during the epitaxial growth of layers by the liquid phase epitaxy technique is presented. An electromagnet is used to keep the hermeticity of the system and to reduce the power requirements of the electrical motor that drives the movements. The core of the electromagnet is coupled to the sliding ruler that contains the substrate through a molybdenum rod. The electromagnet is fixed to a carriage moved by a worm screw that is coupled to the electric motor rotor. The motor is controlled by a system based on a PIC18F4550 microcontroller that works as the host of a LM629, this IC is controls the position, speed and acceleration of devices whose position is given by incremental signals in quadrature. The LM629 generates a trapezoidal signal to perform the movement with a given speed and acceleration. The trajectories are defined in the PC by means of a Lab VIEW program, the data are sent to the PIC18F4550 microcontroller via the USB port that works as the interface between the PC and the LM629.