The ML4640 from Spectrum Control is a RF PIN Diode with Forward Current 10 to 40 mA, Reverse Current 10 uA, Breakdown Voltage 300 to 350 V, Thermal Resistance 25 to 30 Degree C/W, Forward Resistance 1 to 1.3 Ohms. Tags: Surface Mount. More details for ML4640 can be seen below.