Field Emitter Control and Measurement System
The Field Emitter Control and Measurement System (FECMES) provides the capability to control the current generated by a set of field emitter devices and to measure the current leakage to the gate circuits in order to give the total current. Experimental tests using the CFA structure require knowledge of the amount of current entering the channel and the amount of current being reflected back out. Unfortunately the Field Emitter Arrays (FEA) currently available have appreciable amounts of leakage current, diverting a portion of the current entering the emitter away from the channel. A measurement system is required in order to measure this leakage current. The gate current will be the sum of these leakage current values, while the remaining current represents the current into the channel that the emitters are effectively drawing.
The gate structures are biased to a high voltage, anywhere from 0V to 500V. This high bias voltage makes current measurement more difficult. At first it might seem that a low-side current sense would work. While this would be possible with a single gate, it would be expensive with an array of gates. A low-side current sense would require multiple high-voltage power supplies. This technique is limited by the cost constraints of such supplies.
The FECMES system was designed to resolve the issues presented by these high voltages and to provide a control system located at the local ground potential. The control system is then connected to the main host computer using a serial link and high-voltage optical isolators. The host computer uses Lab View for a control environment.