High speed switching circuit

Abstract

A high-speed circuit for causing the corpuscular particle beam of a corpuscular particle microprobe such as a scanning electron microscope to be periodically and sequentially displaced from its normal path so as to, in effect, interrupt the beam's bombardment of a specimen during certain of the scanning cycle of the microprobe. In an elementary form, it includes a deflection circuit having a pair of deflection plates disposed such that the beam passes therebetween and a high-speed driving circuit to power the deflection plates, in order to achieve desired rapid response times. The driving circuit includes a high-speed switch of the type of a vertical MOSFET which is, in turn, connected to a current limiting resistance load which, in turn, is connected to the voltage source for the deflection plates. In an illustrated embodiment, one of the plates is interconnected between the resistive load and the switch such that when the switch is turned from the normal "on" position to the "off" position, the deflection voltage is applied to the plates, through the current limiting resistor; otherwise the switch functions to ground the deflection potential through the switch. The other plate is at ground potential. This high-speed switch is powered by a fast-driving circuit which is responsive to the beam-blanking information signal coming from the synchronization and scan circuitry driving the microprobe or from other logic circuitry. To further enhance the response of the circuit, a second switch is coupled across the load resistor such that this second switch is activated in a transient mode by an RC circuit to provide a low impedance charge-up path to the deflection plate upon the activation of the high-speed switch.

Dependencies are inferred from the claim text.