Semiconductor device circuits

Start of patent duration: 1903 05 15 Longest possible duration:

Issued: 1984 01 25

Inventor:

© dependence:

AT 373 443 © References contemplated by the prior art:

<td>CH-PS</td><td>473478</td><td>CH-PS</td><td>491502</td><td>OE-A</td><td>2060854</td><td>BE-PS</td><td>809216</td>

<td>SE-PS</td><td>809217</td><td>OE-A</td><td>2547303</td><td>CH-PS</td><td>492307</td><td>CH-PS</td><td>484519</td>

<td>OE-A</td><td>2051440</td><td>DE-OS</td><td>2364752</td><td>DE-OS</td><td>2364753</td><td>US-PS</td><td>2822310</td>

<td>CH-PS</td><td>526860</td><td>CH-PS</td><td>474862</td><td>OE-A</td><td>2047342</td><td>GB-PS</td><td>1472113</td>

<td>DE-OS</td><td>2418560</td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>SOLID</td><td colspan="3">STATE ELECTRONICS »BAND</td><td colspan="3">13 (1970) »p. 1025</td><td></td>

- 2 No.373443

The invention relates to a circuit having a semiconductor device, which has on

A) a first zone (emitter zone) of a first conductivity type whose thickness is smaller than the diffusion length of the minority carriers in the same,

B) a second zone (base zone) of a second, opposite to the first conductivity type, which completely surrounds the first zone within the semiconductor device,

C) a third zone (collector zone) of the first conductivity type, which completely surrounds the second zone within the semiconductor device,

D) a fourth zone (injector zone) of the second conductivity type formed in the first zone.

E) first, second and third electrodes disposed on the first, second and third zones, respectively, wherein first and second zones adjoin each other to form a PN junction and a bias voltage source connected to the first and second electrodes and having a forward voltage provides and according to which migrate when polarity of this PN junction in the forward direction majority charge carriers of the first zone via the second zone to the third electrode.

It is well known and common practice to fabricate bipolar transistors in a double-diffusion process which will produce an emitter-base junction for which overall the doping concentration of the emitter is higher than in the base. As this difference becomes larger, the emitter efficiency also becomes higher and approaches more and more the value one. However, with a high doping, the lattice defects and dislocations in the semiconductor substrate also increase. As a consequence of the high doping, the diffusion length of the minority carriers in the doped region decreases. A lowering of the doping, however, leads in previously known transistors to the degree of amplification also decreasing.

In US Pat. No. 2,822,310, inter alia, a transistor is described whose emitter has a high resistivity, that is to say for which the diffusion length is greater than its thickness or width and, moreover, a potential-floating region of the opposite conductivity type is provided which forms a PN junction to the emitter. The said PS states that the number of minority carriers should remain below the equilibrium concentration both in the emitter and in the floating region and that both minority carriers should compensate for the PN transitions. It is also stated that the thickness of the floating held region should be greater than the diffusion length occurring therein so that the minority carrier current in the emitter can be minimized by minimizing the gradient of minority carrier concentration in the floating region. Finally, it is stated in the US patent that the PN junction should be biased in the through-hole direction, otherwise the minority carrier current would increase in each of the regions.

Furthermore, the magazine Solid State Electronics, Volume 13 (1970), page 1025, describes a transistor in which an additional region of the opposite conductivity type is present in the emitter at a distance which lies within the diffusion length of the Minoritäts40 charge carriers in the emitter. The input signal is between the emitter and the additional one

Area supplied while the base is kept floating.

With these known measures in the emitter region, however, no significant improvement in the amplification factor at low noise characteristics and stable operating conditions can be achieved.

The invention is thus based on the object of decisively improving a circuit with a semiconductor component with regard to a high amplification factor, in particular in that the amplification factor can be varied over wide limits. At the same time, the noise characteristics are to be improved, a significantly higher breakdown voltage achieved and a thermally induced deviation of the characteristic values ​​avoided. A further aim is the possibility of incorporation of such a semiconductor device in an integrated circuit together with conventional transistors, in particular also in conjunction with complementary

Transistor pairs.

Based on a circuit of the type mentioned above, this object is erfindungsNr.373443

3 is achieved in that the total thickness of the first and fourth zones is smaller than the diffusion length of the minority carriers in the first zone, the thickness of the fourth zone is smaller than that of the first zone, and a fourth electrode is disposed on and adjoins the fourth zone for the purpose of setting and controlling the gain h ^ g in a wide range a bias source connected, which provides an adjustable bias, wherein the ratio of majority carrier current to input current of the second zone is adjustable by the bias voltage.

In the following, the invention will be described by way of example with reference to the drawings, in which: FIG. 1 shows a section through the semiconductor component of a circuit according to the invention in an enlarged view and FIGS. 2 and 3 show diagrams with characteristics of the semiconductor component shown in FIG.

Before going into the invention in more detail, the operation of a conventional transistor will be briefly described below.

For the current amplification factor α of a transistor in the basic basic circuit, the following applies:

α - α⁺ , ß. γ (1)

Hiebei is a⁺ the collector gain factor, β a base transport factor and γ the emitter efficiency.

First, consider the emitter efficiency γ of an npn transistor. J_n Let the current density be as a result of the electrons injected from the emitter zone into the base region of the transistor and Jp the current density due to the holes injected from the base region into the emitter region of the transistor. Thus, γ results in:

(2)

J + J 1 + J / J η ppn

Let L be the diffusion length of the minority carriers in the base zone; L is the diffusion length of the minority carriers in the emitter zone; D ^ the diffusion constant of the minority carriers in the base zone; D ^ the diffusion constant of the minority carriers in the emitter zone; Np is the concentration of minority carriers in the base zone in the equilibrium state; the concentration of the minority carriers in the emitter zone in the equilibrium state and V the voltage applied to the emitter-base path voltage. This yields the following equations (3) and (4):

^Jn ⁼ qD N np •^xp £ · - * (3)

<td>qD P⁴ pn^v d</td><td>exp</td><td>qj</td><td>•</td><td>(4)</td>

<td>This results in the following equation</td><td></td><td></td><td></td><td></td>

<td>JL</td><td>D</td><td>P</td><td></td><td></td>

<td>P n</td><td>P</td><td>n</td><td></td><td></td>

<td></td><td></td><td>, _</td><td></td><td>(5)</td>

<td>JL</td><td>D</td><td>N</td><td></td><td></td>

<td>np</td><td>n</td><td>P</td><td></td><td></td>

<td colspan="4">When the impurity concentration of the emitter and base regions are ND and NA,</td><td>can Pn / Np</td>

<td colspan="2">be replaced by NA / ND; L_n is from the base width</td><td colspan="2">W limited.</td><td></td>

Nr.373443

ΝΑ

ND (6)

The diffusion constant Dp or D_n is a function of the mobility of the carriers and of the temperature and can therefore be assumed to be approximately constant.

As can be seen from the above equations, the expression δ must be made small to increase the factor ά. In a conventional transistor, this is achieved by making the expression ND very large in equation (6). For this purpose, a double diffusion method is used for the base and emitter zones. However, if the impurity concentration in the emitter zone is selected to be very high, the state of crystallization in the emitter zone and the emitter-base path deteriorates. With Xp as the lifetime of the minority carriers in the emitter zone, the diffusion length Lp results in:

f "(7)

The lifetime x is lowered if the impurity concentration is too high or the state of crystallization is poor or if recombination charge carriers are present. For this reason, the reduction of δ in the equation (6) can not be fully utilized by making ND large since Lp is greatly reduced. In order to increase the upper limit of the factor α, according to the invention, the expression δ is reduced compared to the prior art u.zw. in that the expression L is substantially increased according to equation (6). For example, ND becomes about 5. 10 atoms / cm³ and Lp of about 300 microns are chosen to make the diffusion length of the minority carriers (holes) much larger than in a prior art transistor.

However, if the diffusion length of the minority carriers (holes) in the emitter region is large, another problem arises. If L is greater than the emitter zone thickness, the injected holes at the surface of the emitter zone may recombine and then disappear. As a result, the diffusion length is limited by the thickness of the emitter zone. In an ordinary transistor, L p is smaller than the thickness of the emitter zone. To increase the service life of the minority carriers in the emitter zone, an injector zone formed in the emitter zone is used in a manner known per se, wherein according to the invention the total thickness of emitter zone and injector zone is smaller than the diffusion length of the minority charge carriers in the emitter zone. These measures prevent the value of Lp determined by the impurity concentration of the emitter zone from being reduced by recombination at the surface of the emitter zone.

An exemplary embodiment of a circuit according to the invention implemented in integrated technology is explained in more detail below. In Fig.l -1- denotes a p-type semiconductor substrate layer. On the p-type carrier -1- can be found successively an n⁺-type epitaxial layer -2-, an n-type epitaxial layer -3-, a p-type epitaxial layer -4-, and an n-type epitaxial layer -5-.

The epitaxial layers -2 and 3- serve as the collector region -11-, the epitaxial layer -4- as the base region -12- and the epitaxial layer -5- as the emitter region -13-. Furthermore, in a known manner in the zones -11, 12 and 13- an n⁺-layer -16-, a p⁺-layer -17- and one n⁺conductive layer -18- to the collector, Basisbzw. To make emitter connection. In this example, the impurity concentration of epitaxial layers -4 and 5- became about 10¹⁵ until 10¹⁶ Atoms / cm³ selected. By diffusion of impurities in the emitter zone -13- is in this one injector zone -21- and hiedurch a PN junction 'FE constructed such transistor compared to a transistor without injector zone -21- is very large. In Fig.l is denoted by the reference numeral -14- one of the insulation of the base zone -12- serving by diffusion produced n-type insulating zone and -15- one of the insulation of the emitter zone -13- serving by diffusion p-type insulating zone.

The injector zone -21- shown in Fig.l represents one of the measures mentioned above

Nr.373443

In this case, equation (6), which holds for a one-dimensional model, would have to be corrected by expressions that govern the shape, etc.

take into account the injector zone -21-. This correction is not easy to understand formulaically, but the wiring mechanisms can be explained as follows.

According to the invention, the holes injected from the base to the emitter zone may cause the

PN transition between the injector zone -21- and the emitter zone -13- reach without being attenuated due to the large diffusion length, they then accumulate in the injector zone -21-. When the injector zone -21- is at floating potential, ie can be flooded by charge, its potential increases due to the increase in the holes, the PN junction is forward biased to substantially its ramp voltage and then held constant. As a result, the concentration of holes in the vicinity of the injector zone -21- increases appreciably and the gradient of the hole concentration in the emitter zone becomes much smaller compared to the transistors known today. Since the diffusion current from the base into the emitter zone is proportional to the gradient of the hole concentration in the emitter zone, the current density J becomes very small. Consequently, the electron current occurring at the collector region JP in current components capable of penetrating the emitter region will increase in value, the emitter efficiency will increase according to equation (2), and the factor α will become large.

According to the invention, a potential will be applied to the injector zone -21-. If this potential poles the PN junction to the emitter in the forward direction, then the lifetime 20 of the holes in the emitter zone is large, as if this zone would be at floating potential. If, for example, the injector zone -21- is at the basic quiescent potential of a normal operating point, a high current amplification factor α results. If, on the other hand, the emitter potential or a potential which is negative with respect to the emitter potential is applied to the injector zone, the injector zone operates differently than described above. Namely, the holes injected from the base into the emitter zone are then collected in the injector zone. For this reason, the hole concentration of the emitter zone near the injector zone is greatly reduced. The actual diffusion length of the holes in the emitter zone is limited by the thickness of the emitter zone, so that therein the gradient of the hole concentration and the diffusion current from the base to the emitter zone increases. As a result, the emitter efficiency γ and the current amplification α decrease.

FIG. 2 shows the current amplification factor hgg = - of an emitter-connected transistor, u.zw.

in dependence on the collector current Ιθ. Here, on the abscissa, the collector current 1 ^ in milliamps (mA) and on the ordinate of the current amplification factor h_pE applied, hiebei applies the value of hgg at Ι_β = 0.1 mA as reference value. For the curve B of Figure 2, it holds that the injector 35 zone -21- is connected to the emitter zone, for the curve A, that the injector is at floating potential. From Fig.2 it follows that the current gain hgg according to curve B is lower by about one order of magnitude than according to curve A.

Between the state in which the injector zone -21- is at the same potential as the emitter zone and the state in which it is forward biased, the current 40 gain hgg changes continuously from a low to a high value. The graph of Fig. 3 shows the current gain hgg (ordinate) as a function of Ιθ (abscissa) with the value of a resistor R (not shown) as a parameter placed between the injector zone -21 and the emitter zone, and where V ^ = 3V.

In the p-type injector zone -2 l - kann..auch after a second additional n-type zone (not shown 45) may be arranged. If two such injector zones are adjacent to one another and if they are at floating potential, characteristic curves are obtained between them, as shown in curves A and B of FIG. Furthermore, the current amplification factor hgg, as shown by curve B of FIG. 2, is reduced when the second injector zone is connected to the emitter zone.

It thus follows that by using a transistor according to the invention a

Gain control circuit is constructed which has 'small changes' in the input impedance.

Nr.373443

- 6 With the semiconductor device described above, a thyristor can also be realized. In general, a pnpn thyristor can be considered to consist of an npn transistor, its emitter, base and collector of the cathode, control electrode or the floating base of the thyristor corresponds and a PNP transistor whose emitter, base and collector, the anode, which is located on the floating potential base and the other control electrode of the thyristor. Let the current amplification factor of the npn transistor be α_χ and that of the PNP transistor &lt;χ₂· In this case, the thyristor conducts (the main current) when " ₁ + "₂^&gt;1 and locks (the main stream) when + a ^ l.

The transistor according to the invention with an injector zone can be used as npn part of the thyristor. That is, an additional p-type region is fabricated in an n-type cathode, used as a second gate electrode, and a voltage is applied between the second gate and the cathode, so that the current gain factor .alpha_χ can be regulated. Thus, apart from the usual (first) control electrode, the second control electrode can be used to turn on and off the main current of the thyristor. In this case, the first control electrode for current control and the second control electrode for voltage control. Such a thyristor can be easily constructed from the semiconductor device shown in Fig.l, in which the p-type carrier layer -1- as the anode, the p^-conductive zone -12- as the first control electrode, the n-type conductive region -13- serves as a cathode, and the p-type conductive region -21- serves as the second control electrode.

Hiebei it is possible to form the anode as a Schottky barrier layer (not shown) of a metal, such as aluminum or the like, instead of the p-type zone.

From the above description, it can be seen that, as the first semiconductor region of the first conductivity type, the zone -13-, as the second zone of the second conductivity type the zone -12-, as the third zone of the first conductivity type the zone -11-, as the fourth zone of the second conductivity type the zone -21- can be regarded as the fifth zone of the first conductivity type, the zone arranged in the zone -21- and the sixth zone of the second conductivity type of the carrier -1-.

Only one preferred embodiment has been described above, but the invention is not limited thereto. For example, the invention may be used in semiconductor semiconductor parts of other types, for example pnp transistors, also in modifications, without departing from the scope of the invention.