Electron gun device of field emission type

Claim 2

An electron gun device of the field emission type comprising: a filament of hair pin shape; a cathode tip of needle shape secured to said filament; at least one anode; means for continuously applying an electric voltage between said cathode tip and said anode so as to produce an electric field therebetween which causes electrons to be emitted from said cathode tip toward said anode; and heating power source means for supplying a pulsating current to said filament so as to intermittently heat said cathode tip while the electric field between said cathode tip and said anode is continuously applied, whereby an electron beam emitted from said cathode tip can be stably maintained for a long time.

Claim 3

An electron gun device of the field emission type according to claim 1 wherein the time width of said pulsating current is less than 1 second and the heating temperature of said cathode tip is within a temperature range between 150*C. and 1,000*C.

Claim 4

An electron gun device of the field emission type according to claim 1 wherein said heating power source means includes a pulse oscillator for generating said pulsating current.

Claim 5

An electron gun device of the field emission type according to claim 3 wherein said heating power source means further includes a direct current source, and switching means for switching from the connection between said filament and said direct current source to the connection between said filament and said pulse oscillator and vice versa.

Claim 6

An electron gun device of field emission type according to claim 2 wherein the repetition period of said pulsating current is within an extent of 1 to 20 seconds.

Claim 7

In a scanning type electron microscope including an electron gun device of field emission type; focusing lens means for focusing the electron beam; deflector means for scanning the electron beam on a specimen; secondary electron detector means for detecting secondary electrons; an oscilloscope connected to said detector means so that the intensity of an electron beam therein is modulated by the output of said detector means and having a deflector for scanning said electron beam therein; scanning signal source means for supplying scanning signals to the deflector means and the deflector in said oscilloscope; said electron gun device comprising: a filament of hair pin shape; a cathode tip of needle shape secured to said filament; at least one anode; means for applying an electric voltage between said cathode tip and said anode so as to produce an electric field therebetween which causes electrons to be emitted from said cathode tip toward said anode; and heating power source means for supplying a pulsating current to said filament so as to intermittently heat said cathode tip, whereby an electron beam emitted from said cathode tip can be stably maintained for a long time; and means for controlling said heating power source means to supply said pulsating current synchronously with said scanning to said filament.

Claim 8

In a scanning type electron microscope including an electron gun device of field emission type; focusing lens means for focusing the electron beam; deflector means for scanning the electron beam on a specimen; secondary electron detector means for detecting secondary electrons; an oscilloscope connected to said detector means so that the intensity of an electron beam therein is modulated by the output of said detector means and having a deflector for scanning said electron beam therein; scanning signal source means for supplying scanning signals to the deflector means and the deflector in said oscilloscope; said electron gun device comprising: a filament of hair pin shape; a cathode tip of needle shape secured to said filament; at least one anode; means for applying an electric voltage between said cathode tip and said anode so as to produce an electric field therebetween which causes electrons to be emitted from said cathode tip toward said anode; and heating power source means for supplying a pulsating current to said filament so as to intermittently heat said cathode tip, whereby an electron beam emitted from said cathode tip can be stably maintained for a long time; and means for controlling said heating power source means to supply said pulsating current synchronously with said scanning to said filament.

Claim 9

An electron gun device of field emission type according to claim 6 wherein the pulsive current supplying means includes means for causing the time width of said pulsating current to be within a time required for eliminating a fly-back line of an image on the oscilloscope.

Claim 10

An electron gun device of the field emission type according to claim 7 wherein the time width of said pulsating current is less than 1 second and the heating temperature of said cathode tip is within a temperature range between 150*C. and 1,000*C.

Claim 11

An electron gun device of the field emission type according to claim 8 wherein said heating power source means includes a pulse oscillator for generating said pulsating current.

Claim 12

An electron gun device of the field emission type according to claim 9 wherein said heating power source means further includes a direct current source, and switching means for switching from the connection between said filament and said direct current source to the connection between said filament and said pulse oscillator and vice versa.

Claim 13

An electron gun device of field emission type according to claim 8 wherein the repetition period of said pulsating current is within an extent of 1 to 20 seconds.