Integrated
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Created it, 06/03/17
Update it, 06/03/26
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2. - OTHER LOGICAL FAMILIES
We evoked various technologies implemented to fulfill the switching functions. They are especially those which one most frequently meets.
There are of them others which should be also known, some form already part of the old history.
a) The R.T.L. (resistor - Transistor - Logic), logic with resistances and transistors PNP in negative logic, are completely abandoned.
b) The R.C.T.L. (Resistor - Capacitor - Transistor - Coupled - Logic), logic with resistances and transistors. The integrated capacities were placed in parallel on basic resistances of the transistors in order to improve the speed of transition from the signals.
c) The D.C.T.L. (Direct - Coupled - Transistor - Logic), logic with direct coupling of the transistors.
It is one of the first families, the two preceding ones are derivative.
These technologies were direct applications of the traditional assemblies to discrete components. They practically disappeared today.
However, starting from the bases of the latter (D.C.T.L), one carries out a new technology: the I'I.I.L.
d) The L'I.I.L. (or IČL - Injection - Integrated - Logic) or bipolar logic with injection. It is a recent technology, not very fast whose consumption is very low, which allows a close integration (we will speak about this problem in the chapter concerning the integrated circuits).
This is a major asset in the future of a technology.
e) The T.D.T.L (Tunnel - Diode - Transistor - logic), logic with diodes tunnel and transistors.
The diode tunnel is certainly the fastest device of the commutation which one knows until now. This technology is very little spread and is still the subject of studies.
f) Unsaturated logic :
the C.M.L. (Current
- Mode - Logic), logic with commutation of current.
the C.T.L. (Complementary
- Transistor - Logic), logic with complementary transistors.
the E.C.L. (Emitter
- Coupled - Logic), logic with coupling of transmitters.
These various processes call upon the bipolar transistors.
It is known that a significant part in the limitation of the speed of operation is due mainly to the time put by the transistors to leave the saturated state (storage-time).
Consequently, without touching with the structure even of the transistors, it is enough to modify the point of operation of those by making so that in the conducting state, one avoids the zone of saturation.
Thus, the operators of this technology can function at very high frequencies.
It is currently the logical mode, marketed, fastest.
Unfortunately, its immunity with the noise is very low (from 250 to 500 mV). Its diffusion, to the technicians, is not very important.
According to operators, the travel time varies between 1,5 and 6 nanoseconds.
Consumption is about identical to that of the TTL.
g) Logic with threshold
Still called Threshold-Logic, it is practically not spread, but it exists.
It was conceived for quite specific applications, in the digital circuits with majority decision.
It is founded on the principle of the differential amplifiers, each entry is affected of a different weight (or threshold of tension) and when half of the entries plus one (i.e. majority) is with state 1, the exit changes state.
Several functions are thus fulfilled, but are at the variation compared to Boolean logic (one can say that it is about logic with majority decision).
Moreover, this technology is sensitive to the parasites, especially when the majority of the entries, less one, are already with state 1.
Resistances of polarization of the differential amplifiers must be tight tolerances so that the thresholds are precise, which is an additional handicap with their industrial realization.
h) Devices C.T.D.
These elements with transfer of load (Load - Transfer - Devices) are more especially intended for the registers, with the memories and delay lines, like with the motion-picture devices.
They are founded on the principle of the injection of an electric charge in semiconductor material.
This load is then transferred using an electric field towards the exit.
This electric field is obtained by the application of a system of tensions on grids (identical to those of transistors MOS) distributed along the silicon bar.
According to the distribution of the tensions, the electric field is propagated, involving the load injected with him.
If the field remains motionless, the load remains stored in the silicon bar.
The design of these devices is very simple and allows a close integration. One can, consequently, consider the development of this technology in the fields quoted at the beginning of this paragraph.
| With transistors field effect | With bipolar transistors | With transistors of load CTD |
| P-MOS | R.T.L. | C.C.D. |
| N-MOS | D.T.L. | S.C.T. |
| C-MOS | T.T.L. | B.B.D. |
| E.C.L. | ||
| I.I.L. | ||
| C.D.I. |
3. -
AND THEIR EVOLUTIONINTEGRATED
CIRCUITS
3. 1. - TECHNIQUE CORDWOOD OR FAGGOT
Aviation was one of the first large consumer of electronic material. The imposed requirements obliged the manufacturers to reduce the mass and the obstruction of their apparatuses.
Progress was especially spectacular with the arrival of the semiconductors.
Although the Cordwood technique does not form part of the integrated circuits, it is good to quote it because, certain realization were of a rather exceptional density of components.
This method consists in placing two printed circuits in parallel, one above the other, the faces coppered towards outside. The passive components (in general, resistances) are used of bonds and spacers with the printed circuits.
In an assembly of this kind, conceived well, inside the perimeter delimited by the edges of the printed circuits, it was possible to slip there additional component, such a small was it.
Figure 11 represents, as an indication, a circuit of this kind.
This technique is the starting point of the race towards the miniaturization.
3. 2. - THIN LAYERS
The passive components in the assemblies occupy a very important volume.
In addition, one for a long time knows, to apply lands or insulating to supports called substrates.
Research was thus undertaken to carry out in a reproducible way, on substrate, the passive components necessary to the electronic circuits.
From this moment, we enter the field of the micro-electronics.
The substrates are generally glass or ceramics, on which one deposits successively the layers conducting, resistances or dielectric.
The substrate, mechanical stand of any device, must have :
a dilation coefficient chosen according to the use of the circuit.
a perfect surface quality.
a very high resistivity.
The choice of the deposits is made according to their destination :
gold, copper, for connections
nickel-chromium, oxide of tin, for resistances
glass, silica, for the dielectric ones
silicon, for the semiconductor layers
Various techniques are employed to carry out these deposits. It is :
serigraphy (realized with a silk stencil key set). One will speak rather about thick layers with this process which does not make it possible to reach low thicknesses of deposits.
vacuum evaporation or pulverization
the deposit by gas way
the electrolytic deposit
the chemical plating
In each one of these techniques, the deposits are applied successively thanks to a called important process : technique of the masks.
It consists of one or more maskings by a photoresistive product follow-ups by a chemical attack.
The figure 12-a recalls the various phases of this process.
One deposits on the substrate a first thin layer, then one applies a photosensitive product to this layer.
One then exposes it to an ultraviolet radiation through a mask or film.
After revelation and rinsing of this insolated layer, the subjacent parts which must remain find protected by the photoresistive product.
One proceeds then to a chemical attack, to remove the parts of the deposit which must disappear.
With each deposit of a new layer, one uses the same process by having recourse to a different mask.
The figure 12-b gives an outline of the realization of passive components in technology thin layers (the scales are not respected).
3. 3. - HYBRID
CIRCUITS
The passive components are carried out in thin layers. If one envisages, on these circuits, the sites and connections, one can associate the active components there, such as the transistors and the diodes.
The latter being presented in the form of microcases, they are set up and being welded by microphone-weldings (see figure 13).
By this same process, one can also set up other passive components, as of the condensers whose value cannot be obtained with dielectric materials set up using the deposits.
Small transformers can also be installed in the same way.
It does not remain any more that to protect the whole mechanically, it is encapsulation. The capsule will have to comprise connections of exits.
The size of the hybrid circuits can go from a few millimetres to ten centimetres.
One uses, in general, the flat cases as soon as the size of the circuit reaches 1 to 2 cm. In lower part, one calls standard upon the cases transistors (kind TO3, multiple TO5 at exit).
The technique of the hybrid circuit is very much used in the sets functioning at very high frequency.
Generally, it brings a better output and an increased reliability compared to the traditional circuit (wiring by printed circuit).
It is also used when the monolithic circuit (following paragraph) cannot bring solution, either because the dissipated power is too high, or because it is a question of integrating special components (transformer for example).
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