5. Electronics Repetition from the last lecture • What are the 2 sources of magnetic moment of matter? • What are the macroscopic regions of solids with the same direction of magnetization called? • What happens to the magnetic coercivity of a ferromagnetic particle if its dimensions are reduced below the dimensions of the magnetic domain? What is this phenomenon called? • What is spintronics concerned with? Beginning of Electronics • 1904 – vacuum diode • rectification of the electric current, electrons can only flow in one direction • 1906 – vacuum triode • amplification and control of high frequency signals. Predecessor of the transistor. Diode Triode http://todayscircuits.blogspot.com/2011/06/vacuum-tube-diodes.html#.Y0PGS3ZByJN https://www.eeeguide.com/vacuum-triode-construction-and-working/ Semiconductor Transistor • 1947 – John Bardeen, Walter Brattain, William Shockley (AT&T's Bell Laboratories) - first semiconductor transistor (Nobel Prize 1956) • Two gold strips locally attached to a germanium semiconductor. Current through one contact (emitter-base) amplifies current flowing through the other contact (base-collector). Shockley enhanced the effect by joining layers of germanium with n a p conductivity - creating a PN junction. https://www.nutsvolts.com/magazine/article/the-story-of-the-transistor https://www.edn.com/1st-successful-test-of-the-transistor-december-16-1947/ Semiconductors • Isolants with a narrow band gap (< 5 eV) • InSb (0.23 eV), InAs (0.354 eV), Ge (0.664 eV), Si (1.124 eV), GaAs (1.424 eV), CdTe (1.457 eV), GaN (3.503 eV), V (5.5 eV) • Intrinsic semiconductors conductivity is provided by electrons thermally excited from the valence to the conduction band. A hole (virtual positive charge) remains in the valence band. J. Walker, D. Halliday, R. Resnick, Fundamentals of physics – 10th edition Extrinsic Semiconductors • By using a small amount of impurities (1:106) it is possible to significantly change the electrical conductivity of a semiconductor. • Donor semiconductors • Atoms with an extra electron • Only low energy is needed to release an electron from the donor into the conduction band • Majority carriers are electrons - N-type semiconductor • Acceptor semiconductors • Electron-deficient atoms • Formation of an empty vacancy level in the acceptor atom. Only low energy is needed to excite an electron from the valence band to the acceptor level and to form a hole. This can be occupied by neighbouring valence electrons - the hole will move. • The majority of the charge carriers are holes – P-type semiconductor. Si Si P B N-type semiconductor P-type semiconductor http://conocimientossemiconductorequilibrium.blogspot.com/2010/02/semiconductors.html J. Walker, D. Halliday, R. Resnick, Fundamentals of physics – 10th edition Extrinsic Semiconductors II J. Walker, D. Halliday, R. Resnick, Fundamentals of physics – 10th edition P-N Junction • When we combine P and N semiconductors, the moving electrons and holes diffuse into an adjacent type of semiconductor where they recombine. Leaving behind the immobile impurity ions. This creates a depletion region in the transition region without free charges, where there a permanent electric field arises (space charge region). https://www.researchgate.net/figure/p-n-junction-When-a-metallurgical-junction-is-formed-between-an-n-type-and-a-p-type_fig3_279810779 Contacting the P-N Junction • Contacting in the forward bias • Semiconductor P is connected to + and semiconductor N to • We „dope" semiconductor P with holes and N with electrons, which recombine with ions in the transition region and make this region thinner. Electron and hole currents can then pass through • Contacting in the reverse bias • Semiconductor P is connected to and semiconductor N to + • Electrons are attracted to the + pole of the source and holes to the – pole of the source. The depletion region is enlarged. Current does not flow. https://www.electrical4u.com/pn-junction/ I-V Characteristic of the Diode • Forward bias • Reverse bias • Remark: • If charge recombination in the transition region is associated with photon emission - LED (light emitting diode; GaAs, GaP, GaAsP). The N semiconductor is typically more doped than the P one. • If the impact of a photon creates an electron-hole pair in the P-N transition region, which is then sepparated by permanent voltage in the transition region - a photovoltaic cell https://theengineeringmindset.com/the-basics-of-diodes-explained/diode-iv-2/ Bipolar Junction Transistor • Transistor = transfer + resistor • 2 PN junctions (NPN or PNP) • NPN - heavily doped N emitter region, weakly P doped base, weakly N doped collector • Electrons accelerated by voltage VBE penetratethrough the weakly doped base. Due to the weak doping amd a small thickness of the base, only a small number of electrons recombine there. A large number (> 90%) of electrons pass through the base into the collector region where they are further accelerated by voltage VCB. This reduces the electrical resistance in this region. • With a small voltage/current we are able to control large currents emitter collector base https://en.wikipedia.org/wiki/Bipolar_junction_transistor MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) • Slightly p-doped substrate, n doped islands S (source) and D (drain) and a narrow channel between them. On the substrate there is a thin non-conducting layer of SiO2 through which the metal contacts to S and D lead. • If VGS voltage is not applied, current ("1") flows between S and D. If it is applied with opposite voltage polarity on the transistor to the substrate (- for a P-doped substrate), this voltage will repel electrons from the channel down to the substrate. This will increase the natural depletion region between the P doped substrate and the N doped channel, which is "pinched". At sufficient voltage, the channel closes and no current ("0") flows between S and D. • No current flows between G and the substrate - no current and energy losses. • The basis of computer chips. • Due to the thickness of the n channel, the MOSFET is a nano- (quantum) component https://www.rs-online.com/designspark/what-is-mosfet-a-detailed-guide-on-mosfet J. Walker, D. Halliday, R. Resnick, Fundamentals of physics – 10th edition Microelectronics – CMOS (Complementary MOSFET) • Transistors can be used to construct logic circuits (logic gate) NMOS NMOS 2x PMOS NAND Gate A B NAND out 1 1 0 1 0 1 0 1 1 0 0 1 https://en.wikipedia.org/wiki/CMOS CMOS – Layout • The individual areas are prepared on a silicon wafer in several layers https://bsse.ethz.ch/research/facilities/cleanroom-facility.html https://en.wikipedia.org/wiki/CMOS CMOS Production • Production consists of many sub-steps (top-down) • Thermal oxidation of wafer • Chemical/physical substrate etching • Diffusion of donor • Chemical/physical etching of oxide • Oxidation for gate • Deposition of gate material • Etching of gate https://en.wikipedia.org/wiki/CMOS CMOS Production II • Donor and acceptor implantation into Source and Drain • Deposition of protective nitride • Nitride etching • Metal deposition • Etching of metal contacts https://en.wikipedia.org/wiki/CMOS Limits of Current Technology • By thinning the SiO2 layer to a few nm we lose its insulating properties • By shrinking the structures, the original band structure is lost (change in electrical conductivity) • Due to the low concentration of impurities, the individual structures are no longer the same in nm3 • The cost of production increases (cleanliness of the environment, materials, lithographic techniques) • Non-standard phenomena in nanostructures – ballistic collisionless charge transport • Heat loss (more than 100W/cm2) https://en.wikipedia.org/wiki/Microprocessor_chronology Nanoelectronic Components • Tunnel diode • Very fast switching diode (< 100 ps), high frequency oscillator, damping suppression in oscillator circuits • Typically made of very heavily doped germanium, resulting in a small pn transition region • Double-barrier resonant-tunneling diode • High speed switching, oscillators and switches up to THz frequencies • Transition coefficient non-monotonically depends on electron energy – for certain energies this barrier is completely transparent – tunneling will always occur https://www.theengineeringknowledge.com/introduction-to-tunnel-diode/ https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr201110fa2.html Nanowire FET Transistors • Further miniaturization of transistors. • The current between source and drain flows through nanowires. • A new building block for future chips https://spectrum.ieee.org/nanowire-transistors-could-keep-moores-law-alive JP Colinge, JC Greer, Nanowire transistors,Cambridge University Press 2016 Single Electron Transistor – SET • 1 bit = 1 electron • The electron going from source to drain must pass through a double quantum tunneling through a quantum nanoparticle (quantum dot; Coulomb island), which is separated from both S and D by about 1 nm of insulator • Works on the principle of Coulomb blockade • For a reliable SET function, different dots in different transistors need to have the same capacitance. We cannot provide this yet . • ΔE = e2/C 0 1 https://en.wikipedia.org/wiki/Single-electron_transistor JP Colinge, JC Greer, Nanowire transistors,Cambridge University Press 2016 SET https://www.intechopen.com/chapters/8670 JP Colinge, JC Greer, Nanowire transistors,Cambridge University Press 2016 Molecular Electronics • Electronic circuits made from molecules could solve many of the problems of silicon technology, such as the reproducibility of small structures. They are also flexible. • In the 1970s – the first theoretical design of a diode molecule • First preparation 1997 • Polyphenylene chains (a chain of benzene nuclei lacking 2 hydrogens) and carbon nanotubes are most often investigated as conductors – Aliphatic hydrocarbons (without benzene nucleus) are investigated as insulators Diode Double resonant tunneling diode https://www.researchgate.net/publication/32897030_Fault_tolerance_issues_in_nanoelectronics https://www.researchgate.net/publication/51988506_A_New_Full_Adder_Cell_for_Molecular_Electronics Logic Gates for Computers https://www.researchgate.net/publication/323500234_Molecular_logic_gates_The_past_present_and_future Conclusion • What is and how does PN transition work • What is a diode, transistor, MOSFET • How transistors are applied in logic chip design • Manufacturing chips • Physical limitations of current technologies • Some nanoelectronic components • Molecular electronics