Presentation on theme: "THE PLANAR DEFLECTRON Geoffrey H. Grayer BSc PhD"— Presentation transcript:
1THE PLANAR DEFLECTRON Geoffrey H. Grayer BSc PhD A micro-engineered amplifier and logic device.
2Contents Introduction - what is planar deflectron? Principles of operation; Switch and AmplifierEvolutionPlanar Construction and FabricationUnique special featuresIPR positionSeed funding objectivesSummary
3IntroductionThe Deflectron idea is being developed at the Rutherford Appleton Laboratory by a collaboration between the Detector Group of the Instrumentation Department and the Central Microstructure Facility.I was the instigator of the idea, but it is of course a team effort, with particular thanks to Bob Stevens, Zheng Cui and Ejaz Huq.
4What it is -A vacuum device (like a sub-miniature tube/valve) which acts as an amplifier or logic elementIt uses field emission instead of a heated cathodeIt deflects the electron path rather than trying to modulate the current (like a television tube)= DeflectronIt is constructed in one plane for simplicity and connectivity= Planar
5Principle of Operation Extractor produces high electric field on cathodeHence cathode emits electrons according to the Field EffectA triplet of focus electrodes alter final spot sizeSignal applied to deflection plates move beamSplit anode collects electronsConventional construction would work from the tip up, using cylindrical symmetryModel by Z. Cui showing electron tracks for one set of parameters.
6How it evolvedFor at least 20 years people have been trying to realise a field-effect amplifierUsually an attempt has been made to produce the analogy of a triode vacuum tube with a 3-D cylindrical shape (see fig)They have not worked because the potential of electrons produced by a field emitter is typically x100 that of a thermionic emitter, reducing gain by that amount. Hence typical valve stage gain 30 becomes 0.3 !A scanning electron microscope picture of a conventional 2- gate field emitter. This represents “state of the art” (photo CLRC)
7The Noise IssueThe variation in emission current is typically 10% from a field emitter. This is noise superposed on the signal, and would make any amplifying application untenableMy solution to this is to create 100% feedback by adding a suitable resistor in the cathode circuit (R=dVg/dIa)Having fixed the current one cannot amplitude modulate the electron beam. The solution is to deflect it - hence the name Deflectron!
8Conventional 3D Cylindrical Construction 3D device fab would be extremely complex, requiring many processes to build up the structureThis gets even more difficult when the focus and deflection electrodes are added, breaking cylindrical symmetry.When anodes added on top, closed volume is almost impossible to evacuate.They are difficult to connect with electrodes all at different levelsA scanning electron microscope picture of a conventional 2- gate field emitter. This represents “state of the art” (CLRC device)
9Planar ConstructionTo see how the planar device evolved, imagine a slice taken through the middle of the cylindrical device.Construction is then simple lithography of metal, plus the tip fabrication.Simplified layoutof Deflectron
10Fabrication issues Single layer device -planar Critical process is production of pointed cathode emitter in planePrinciple yield defining step:Direct EBL defines point in planePlasma etch defines point at right angles to planeAll other fabrication processes are ‘conventional’ VLSI patterning in refractory metal
11Schematic Diagram A1, A2: anodes D1, D2: deflector F1: focus H F2: focus VF3:focus HE: extractorK: field emitting cathode
12Characteristics of Planar Deflectron Can work as amplifier or logic elementAmplifier has gain/dynamic range trade-off, set by voltage parametersSmall size means very fast (fo = 1~10GHz)Complementary signals in/out with high common mode rejection - benefit is external noise/spike rejectionCoupling can be DC as only reacts to voltage difference benefit - broadband operation to10GHzPower consumption very low and independent of speed or stateSimple few-step fabrication
13The Deflectron as Logic Element Focused to a spot, the current rapidly changes from one anode to another, producing the ideal binary switchThese switches may be connected in series to carry out the usual Boolean logic functionsA tri-state device may be produced by introducing a third central anode which is connected straight to +V. Thus devices can be multiplexed to the same bus.Tri-state device
14The Deflectron as Amplifier Defocused at the anode, the current varies slowly as the beam is deflected, resulting in a analogue amplifierBy varying the spot size, gain is traded against dynamic range, according to application
15Gain of the Deflectron The Gain of the Deflectron depends on: ~ 1/ extractor voltage (“stiffness”)~ integrated deflecting E-field:~ Length of deflector plates~ 1/ Spacing of deflector plates~ drift length (“lever arm”)~ spot size (adjustable by focus)(In principle, there is no limit on the drift length.)
16Unique Special Features This is not expected to replace the ubiquitous transistor, but to go where no transistor dares!It will work at very high temperatures - eg NASA Venus lander ? (max. is melting point!)It will work at temperatures approaching absolute zero - eg quantum microdot readout(This could be important commercially)It will work in very high radioactivity - eg particle physics experiments, nuclear industryIt has high noise rejection because of complimentary in/out signals
17IPR: The idea of deflecting electrons is not new It looks like a miniature electrostatic CRT, with the screen replaced by anodesDeflection - modulated electronic tubes (valves) were made and patented by RCA in the 1960s. Their high dynamic range made them excellent mixers.Its use as a vacuum micro-electronics device for generating microwaves has been suggestedHowever, this particular application and the planar construction are novel
18IPR position No filings submitted to-date Public disclosure in scientific publication: Technical Digest, 10th International Vacuum Microelectronics Conference, August 17-21,1997, Kyongju, S. Korea, p.206, G.H.Grayer, S.E.Huq, Z.Cui, P.D.PrewettIf go-ahead, need urgent review ofWhat may be protectedSearch of existing IPR in the field
19Seed funding objectives Identify & complete PCT patent applications to secure IPR of embodiment & fabrication processesDefine & characterise pointed cathode processDemonstrate field emission from pointed cathode + incorporation in planar device structureProduction of planar deflectron demonstratorCharacterisation of complete fab process stepsElectrical characterisation of proof-of-principle demonstrator
20Seed funding required to produce proof-of-principle demonstrator Estimated £70k
21Summary The Deflectron is: A very wide band amplifier or switch (0 to many GHz)Capable of operating over extremes of temperature (cryogenic to high temperatures)Extremely radiation hardExtremely resistant to EMIVery ruggedSimple and hence cheap to construct (= high yield)Could be realised with a relatively low capital investment