According to one embodiment, a semiconductor memory device includes a command processing module, a plurality of storage units, a plurality of control modules, an adjustment circuit, and a setting register. The voltage waveform has four intervals. A semi-permeable layer may be attached to the outer surface of the porous layer to prevent erosion of the porous layer and to facilitate surface film cooling. The wireless communication device remotely controls the robot refrigerator, or monitors or remotely controls the robot refrigerator in real time, so that the robot refrigerator easily avoids an obstacle, and thus, minimizes a movement time of the robot refrigerator.