Field effect semiconductor device having an unsaturated triode vacuum tube characteristic

Abstract

A field effect transistor comprises a semiconductor channel, a source and a drain electrode formed at the opposite ends of the channel and a gate electrode provided on the side of the channel. The channel has a small impurity density and therefore the depletion layer extending from the gate goes deep into the channel to substantially close the conductive portion of the channel even in the absence of a gate voltage. The drain current will not flow where the drain voltage is below a certain threshold voltage, and will flow where the drain .[.volage.]. .Iadd.voltage .Iaddend.is above the threshold voltage exhibiting a .Iadd.substantially .Iaddend.linear resistance characteristic. This drain-current to drain-voltage characteristic simulates the anode-current to anode-voltage characteristic of the triode vacuum tube very closely.

We claim: 
     
       1. A field effect semiconductor device capable of exhibiting unsaturable drain voltage versus drain current characteristics comprising: a first and second spaced gate region formed of a relatively high impurity doped semiconductor material and having a first conductivity type;   a semiconductor region located adjacent to said first and second spaced regions and having an opposite conductivity type, said .[.second.]. .Iadd.semiconductor .Iaddend.region being formed of a substantially intrinsic semiconductor material of a low carrier concentration, said semiconductor region having a portion forming a current channel between said first and second gate regions, said channel including the semiconductor region disposed between respective junctions formed with said first and second gate regions defining the sides of said channels and including a depletion layer incident to each of said junctions, said depletion layers being contiguous or overlapping each other to achieve a pinch-off condition within said channel in the absence of a reverse bias voltage applied to said first and second gate regions;   a source region located along said channel for supplying a current thereto;   a drain region spaced from said source region along said channel for providing an output current, said source region and drain region comprising semiconductor regions having the same conductivity type as said channel region;   gate biasing means for applying a reverse bias voltage to said first and second gate regions to increase the effective length of the overlapping depletion layers along said current channel with an increase in magnitude of the applied reverse bias voltage to thereby determine a threshold drain voltage,   wherein the application of a drain voltage greater than said threshold voltage allows the carriers from the source region to travel toward said drain region in the depletion layer existing along the current channel in the same manner as that exhibited by a triode vacuum tube.   
     
     
       2. The field effect semiconductor device of claim 1, in which the extent of the depth of said depletion layers is determined by the contact potential at said junction and by the impurity concentration of the semiconductor material of the channel region, wherein the gate-to-gate distance is determined. 
     
     
       3. The field effect semiconductor device of claim 1, in which the output current at said drain region exhibits an unsaturated non-linear characteristic with respect to the applied drain voltage when said drain voltage is above a threshold determined by a given gate bias voltage. 
     
     
       4. The field effect semiconductor device of claim 1, in which said channel constituting the semiconductor region is formed of a plate elongated in the source-to-drain direction, and said first and second gate regions are formed on the two principal surfaces of said plate sandwiching therebetween said current channel, the depletion layers extending from said gates and contacting or overlapping each other. 
     
     
       5. The field effect semiconductor device of claim 4, in which each of said gate electrodes has a dimension in the longitudinal direction along said current channel small enough to reduce the series resistance of the channel. 
     
     
       6. The field effect semiconductor device of claim 1, in which said source and drain regions and said gate regions are disposed on one surface of the semiconductor material constituting the current channel. 
     
     
       7. The field effect semiconductor device of claim 1, in which said channel constituting semiconductor material is silicon having an impurity concentration below the order of 10 15  /cm 3 . 
     
     
       8. The field effect semiconductor device of claim 4, in which said current channel between the gate regions has a diametrical dimension of at most three times the total width of the total depletion layers calculated from the assumption of perfect ionization in the depletion layers. 
     
     
       9. A field effect transistor according to claim .[.1.]. .Iadd.19.Iaddend., wherein said semiconductor substrate is cylindrical and the gate electrode has a hollow cylindrical shape formed on the side surface of said cylindrical substrate surrounding the current channel extending therewithin. 
     
     
       10. A field effect transistor according to claim .[.1.]. .Iadd.19.Iaddend., wherein said gate electrode is annular and surrounds the source electrode. .[.11. A field effect transistor according to claim 1, wherein said semiconductor substrate is cylindrical and said gate electrode is formed 
     
     
        on an intermediate portion of the side surface of said cylinder..]. 12. A field effect transistor according to claim .[.1.]. .Iadd.19 .Iaddend.wherein a plurality of said gate regions are formed in and traversing the current channel. .Iadd. 13. A field effect semiconductor comprising a semiconductor region formed of a substantially intrinsic semiconductor material having a low carrier concentration,   at least one source region of a predetermined conductivity type adjacent to said semiconductor region,   at least one drain region of said predetermined conductivity type adjacent to said semiconductor region, removed from said source region, thereby constituting in said semiconductor region a current path from said source to said drain, and   at least one gate structure connected to said semiconductor region to form a depletion layer in said semiconductor region extending from said gate which substantially occupies a whole cross-section of said current path in the absence of a gate voltage, said depletion layer being of minimum   
     
     
        effective size in the absence of said gate voltage. .Iaddend..Iadd. 14.  A field effect semiconductor device comprising a semiconductor region formed of a substantially intrinsic semiconductor material having a low carrier concentration,   at least one source region adjacent to said semiconductor region,   at least one drain region adjacent to said semiconductor region, removed from said source region, thereby constituting in said semiconductor region a current path from said source to said drain, said source and drain regions being heavily doped and of the same conductivity type, and   at least one gate structure connected to said semiconductor region to form a depletion layer in said semiconductor region extending from said gate which substantially occupies a whole cross-section of said current path in the absence of a gate voltage, wherein the application of a drain voltage greater than a threshold voltage forces the carriers from the source to travel toward said drain along said current path through said depletion layer to thereby provide a current-voltage characteristic similar to that   
     
     
        of a vacuum tube triode. .Iaddend. .Iadd. 15.  A field effect semiconductor device comprising a semiconductor region formed of a substantially intrinsic semiconductor material having a low carrier concentration, said carrier concentration being less than 10 15  /cm 3 ,   at least one source adjacent to said semiconductor region,   at least one drain adjacent to said semiconductor region removed from said source region, thereby constituting in said semiconductor region a current path from said source to said drain, said source and drain regions being of the same conductivity type, and   at least one gate connected to said semiconductor region to form a depletion layer in said semiconductor region extending from said gate which substantially occupies a whole cross-section of said current path in the absence of a gate voltage, wherein upon the application of a reverse bias gate voltage, a threshold voltage is defined above which a drain voltage forces carriers from the source toward said drain through said depletion layer occupying a whole cross-section of said current path to thereby provide a current-voltage characteristic similar to that of a vacuum triode. .Iaddend..Iadd. 16. A field effect semiconductor device capable of exhibiting unsaturable drain voltage versus drain current characteristics comprising:   a substantially intrinsic semiconductor region;   source and drain semiconductor regions, said source and drain regions being highly doped and of the same conductivity type, and being disposed contiguous to said intrinsic region, said source and drain regions defining a current path therebetween through a portion of said intrinsic region; and   gate means for controlling current through said current path in accordance with a gate voltage applied thereto, carriers flowing along said path from said source to said drain when the voltage at said drain exceeds a predetermined threshold value;   said gate means including contact potential producing means contiguous to said intrinsic region for generating, in the absence of a gate voltage applied to said gate means, a potential at the junction of said potential producing means with said intrinsic region, said potential producing a depletion layer extending across substantially an entire cross-section of said current path such that said carriers flowing along said current path must pass through said depletion layer, said depletion layer increasing in effective size in response to increasing magnitude of said applied gate voltage to determine thereby said threshold drain voltage value. .Iaddend..Iadd. 17. The device of claim 16 wherein said gate means comprises:   a layer of insulator material, one surface thereof adjacent said intrinsic region; and   a metallic electrode disposed on the surface of said insulator layer opposite said one surface. .Iaddend. .Iadd. 18. A field effect semiconductor device capable of exhibiting unsaturable drain voltage versus drain current characteristics comprising:   a gate region formed of a relatively high impurity doped semiconductor material and having a first conductivity type;   a semiconductor region located adjacent to said gate region and having a second conductivity type opposite said first conductivity type, said semiconductor region being formed of a substantially intrinsic semiconductor material of a low carrier concentration;   a source region formed of a relatively high impurity doped semiconductor material and connected to said semiconductor region;   a drain region formed of a relatively high impurity doped semiconductor material and connected to said semiconductor region;   said source and drain regions defining a current path therebetween through said semiconductor region, current flowing from said source to said drain along said current path in response to a drain voltage in excess of a predetermined threshold voltage;   said semiconductor region including a depletion layer incident to said gate region, said depletion layer forming a pinched-off area within said path in the absence of a reverse bias voltage applied to said gate region;   means for applying a reverse bias voltage to said gate region to increase the effective length of the depletion layer forming said pinched-off area along said current path in accordance with an increase in magnitude of the applied reverse bias voltage, to define thereby said threshold drain voltage whereby the application of a drain voltage greater than said threshold voltage forces carriers from the source region to travel toward   
     
     
        said drain region through said depletion layer. .Iaddend..Iadd. 19.  A field effect semiconductor device capable of exhibiting unsaturable drain voltage versus drain current characteristics comprising: at least one gate region formed of a relatively high impurity doped semiconductor material having a first conductivity type;   a semiconductor region located adjacent to said gate region and having a second conductivity type which is opposite to said first conductivity type, said semiconductor regions being formed of a substantially intrinsic semiconductor material of a low carrier concentration;   a source region formed of a relatively high impurity doped semiconductor material and connected to said semiconductor region;   a drain region formed of a relatively high impurity doped semiconductor material and connected to said semiconductor region;   said source and drain regions defining a current path therebetween through said semiconductor region, current flowing from said source to said drain along said current path when the voltage at said drain region exceeds a threshold drain voltage;   said semiconductor region having a portion forming a current path, said path including the semiconductor region disposed between the junction formed with said at least one gate region and including a depletion layer incident to said junction, said depletion layer forming a pinched-off area within said current path in the absence of a reverse bias voltage applied to said gate region; and   gate biasing means for applying a reverse bias voltage to said at least one gate region to increase the effective length of said depletion layer along said current path in accordance with an increase in magnitude of the applied reverse bias voltage, to determine thereby said threshold drain voltage, whereby the application of a drain voltage greater than said threshold voltage forces carriers from the source region to travel toward said drain region through said depletion layer in the same manner as that exhibited by a triode vacuum tube. .Iaddend.