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Transistors - die pictures

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I've suspected that they gave up on the HEXFET pattern a long time ago; it's possible they went with stripe (as basically? everyone else has) since, perhaps just the first generation or three even?  The name might then remain as the internal name for the chain of development, or as an IP scheme (trademark and related patents?).  All 2nd-source / substitute parts call theirs "planar stripe" or something to that effect, which I wonder if it was (at first?) a patent-evasion strategy, or just more suitable to their existing processes, or in fact the better way and everyone's converged on it now.  Well, the latter seems likely, heh.


I had the same thoughts. Probably they changed the architecture and didn´t update the datasheet because for most people the electrical specifications are important not the architecture.  :-+

First additional information about the IRF3708:
It seems our thoughts were correct: International Rectifier changed their HEXFETs to "planar stripe HEXFET":

Next: The Signetics NE543 is a servo motor driver. It supposedly corresponds to the WE3141, which was distributed by World Engines, a company from Cincinnati manufcaturing model kits. Perhaps the WE3141 was developed with Signetics and was later incorporated into the Signetics portfolio as the NE543.

There is a die in the housing, which also has bondpads in the centre. At the left edge of the die, you think you can recognise an image defect. However, this is actually a surprisingly wide edge.

It is difficult to visualise how slanted the edge actually is. It appears that the wafer was only cut very shallow and the rest was broken.

The dimensions of the die are 2,0mm x 1,8mm. On the right edge the characters 916A A are shown, presumably an internal project designation.

The datasheet shows a block diagram of the module and how it is usually wired. It is controlled with a square-wave signal via pin 4. The pulse width of the square-wave signal defines the setpoint position of the servomotor. Two inverters (yellow) process the input signal. The outputs of the inverters control a flip-flop (green) and are linked to the outputs of the flip-flop via NAND gates (purple). The lever of the servomotor is connected to a potentiometer. Depending on the current resistance value, the flip-flop generates pulses of different lengths. As a result, the NAND gates output pulses that are proportional to the deviation between the setpoint value and the actual value.

The NAND gates are followed by two circuits that extend the pulses of the flip-flop (cyan). The resistors Rs1 and Rs2 define by how much the pulses are extended. The resistors Rd1 and Rd2 ensure that the servomotor is only activated when there is a certain deviation between the setpoint and actual value. Finally, a second flip-flop (blue) realises the control of the two motor drivers (red), which represent an H-bridge. The resistors R8 and R9 improve the control behaviour of the circuit.

The datasheet also contains a circuit diagram of the module. The individual function blocks are highlighted here in the appropriate colours. An error has crept into the second buffer amplifier. Transistor Q2 has to be an NPN transistor. The circuit is largely self-explanatory. The only noticeable feature is the quadruple base contacting of the lowside transistors Q26/Q27 in the H-bridge.

The large H-bridge takes up more than half the area of the die. The transistors at the outputs of the pulse stretcher are just as prominent.

A closer look at the H-bridge shows that the circuit diagram does not quite reflect reality. The lowside transistors Q26 and Q27 each consist of two transistors. It is logical that each transistor has its own base resistor. However, it remains unclear why two base resistors have been integrated for each transistor.

The highside transistors Q24 and Q25 also each consist of two transistors. A PNP driver transistor is assigned to each highside transistor. However, the base potentials of the highside transistors are also connected in pairs.




The 2N3878 is a fast NPN power transistor in a TO-66 package. It blocks up to 50V, whereby the collector-base blocking voltage is significantly higher at 120V. The collector current may be 4A continuously and 10A for short pulses. With a collector current of 4A, the amplification factor is still at least 20. Up to 35W can be dissipated through the housing. The cut-off frequency is specified at 40MHz. At 4A, the 2N3878 enables switching pulses with a duration of 1µs.

The advertisement shown here is from the magazine Electronics from 1965.

The transistor is placed on an unusual heatspreader. The electrical contact is made with sheet metal elements that have been pushed onto the pins and then have been soldered to them.

The heatspreader appears to have been soldered into the base plate.

The contact plates are soldered directly to the die. The base potential (on the right side) is fed into the emitter surface via the metal layer. These conductor tracks are slightly thinner than those of the emitter. The entire structure is coated with a clear protective lacquer.

The transistor has a MESA structure with edges that are not completely straight. The surface of the transistor is partially irregular. A faintly recognizable edge separates the emitter area from the base area.

The surface is damaged in one spot. This appears to be a scratch that extends from the upper line of the emitter area to the lower line of the base area. In the lower area, the silicon is also damaged in addition to the metallization. However, the damage does not extend to the junction.

The base-emitter junction breaks down at -9V. The avalanche breakdown produces the familiar glowing dots. The current increases as follows: 10mA / 20mA / 30mA / 40mA / 50mA / 100mA / 200mA / 300mA / 400mA / 500mA

The light develops very evenly. However, the scratch seems to have an effect on the electric field. Below this artifact, the light spreads out late. In the lower left corner there are hardly any glowing islands. Since the metal layer with the base potential does not extend into this area, the resistance of the base-emitter path is higher there and the breakdowns in the areas with lower resistance remain dominant.

The infrared image shows the relationships that are described in more detail with the SF137 (https://www.richis-lab.de/Bipolar75.htm). In this image, the base current is 1A, while the collector current increases like this: 1A / 2A / 3A / 4A / 5A / 6A / 7A. The light initially only appears under the base area. As the collector current increases the light moves towards the emitter.

In this picture, the base current is just 0,5A. While the collector current rises to 8A, the transistor leaves the saturation area. The resulting high thermal load ultimately destroys the structures, which is shown by the emitter contact lighting up.

The damaged area can only be guessed at by a small discoloration. The protective lacquer, which is torn at the emitter contact, disturbs the view on the surface of the transistor.




The International Rectifier IRLZ44 is a power MOSFET whose reverse voltage is specified at 60V. With a typical resistance of 28mΩ, a continuous drain current of 50A is permissible at room temperature. The IRLZ44 is a logic-level MOSFET. It achieves the resistance of 28mΩ at a gate-source voltage of 5V. For a gate-source voltage of 4V, the data sheet still specifies 39mΩ.

The marking can only be read easily with the correct illumination. The syntax and the layout of the marking match the representations often found in International Rectifier datasheets.

The die of the IRLZ44 is 3,6mm x 2,8mm. The gate potential is contacted on the left. The metal layer conducts the potential around the circumference of the transistor and also a little way into the center of the surface via two stubs.

As with many transistors from International Rectifier, several masks with numbers are shown on the upper edge. However, the structures are difficult to recognise here.

In the center of each edge is a small square of the metal layer. The purpose of these squares remains open, perhaps they facilitated the alignment of the masks or made it possible to check the alignment later.

A honeycomb structure can be seen in detail on the surface of the drain metal layer.

There is an older datasheet for the IRLZ44, according to which it is a third-generation HEXFET. In this datasheet, however, the device was not yet lead-free and lacked the index N. The P of this IRLZ44 shows that it is a lead-free device. An N is also appended to the designation. A more recent datasheet, which matches this marking, attributes the IRLZ44 to the fifth generation of HEXFETs. In any case, the honeycomb structure corresponds to the surface shown in the "International Rectifier HEXFET Databook".




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