CA1232974A - High speed diode - Google Patents
High speed diodeInfo
- Publication number
- CA1232974A CA1232974A CA000424725A CA424725A CA1232974A CA 1232974 A CA1232974 A CA 1232974A CA 000424725 A CA000424725 A CA 000424725A CA 424725 A CA424725 A CA 424725A CA 1232974 A CA1232974 A CA 1232974A
- Authority
- CA
- Canada
- Prior art keywords
- layer
- diode
- pnn
- thickness
- current
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000000758 substrate Substances 0.000 claims abstract description 11
- 238000000407 epitaxy Methods 0.000 claims abstract description 4
- 239000000969 carrier Substances 0.000 claims description 15
- 238000009792 diffusion process Methods 0.000 claims description 5
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 4
- 239000010931 gold Substances 0.000 claims description 4
- 229910052737 gold Inorganic materials 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 4
- 229910052697 platinum Inorganic materials 0.000 claims description 2
- 230000007423 decrease Effects 0.000 description 4
- 230000000903 blocking effect Effects 0.000 description 3
- 238000011084 recovery Methods 0.000 description 3
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 230000005684 electric field Effects 0.000 description 2
- 230000010355 oscillation Effects 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- NLZUEZXRPGMBCV-UHFFFAOYSA-N Butylhydroxytoluene Chemical compound CC1=CC(C(C)(C)C)=C(O)C(C(C)(C)C)=C1 NLZUEZXRPGMBCV-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 239000002019 doping agent Substances 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 244000045947 parasite Species 0.000 description 1
- QHGVXILFMXYDRS-UHFFFAOYSA-N pyraclofos Chemical compound C1=C(OP(=O)(OCC)SCCC)C=NN1C1=CC=C(Cl)C=C1 QHGVXILFMXYDRS-UHFFFAOYSA-N 0.000 description 1
- 230000006798 recombination Effects 0.000 description 1
- 238000005215 recombination Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/36—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the concentration or distribution of impurities in the bulk material
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
- H01L29/861—Diodes
Landscapes
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Ceramic Engineering (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Bipolar Transistors (AREA)
- Thyristors (AREA)
- Bipolar Integrated Circuits (AREA)
- Electrodes Of Semiconductors (AREA)
Abstract
A HIGH SPEED DIODE
ABSTRACT OF THE DISCLOSURE
A PNN+ high-speed diode comprising, bet-ween the usual layers, an additional layer disposed between the N+ layer and the N layer. This additional layer and the N layer are obtained by epitaxy on the substrate. Said additional layer has a doping level intermediate between those of the N and N+ layers.
ABSTRACT OF THE DISCLOSURE
A PNN+ high-speed diode comprising, bet-ween the usual layers, an additional layer disposed between the N+ layer and the N layer. This additional layer and the N layer are obtained by epitaxy on the substrate. Said additional layer has a doping level intermediate between those of the N and N+ layers.
Description
~3~
]
BACKGROUND ~F THE INVENTION
The present invention relates to a high speed diode capable for example of providing a rectifying or free-wheel diode function in a chopper circuit.
More particularly, ~he invention provides such a diode having improved characteristics during switching from the conducting to the ~locking state, that is to say a better switching off characteristic.
Although this aspPct i6 not developed herea it should be noted generally that a diode having good switching off characteristics also has better switching on characteristics.
To give a better understanding of the present invention, the principal parameters characterizing the switching off of a diode will first of all be ~efined. Certain theoretical explanations will also be recalled concerning the physical phenomena occurring during switching off. Nevertheless, even if the present theories prove to be wrong, the diode of the invention is defined by its structural characteristics and an error in the theoretical explanations could have no influence on the present invention whose advantages have been proved experimentally.
Figures 1, 2 and 3 characterize conven~ional high-speed diodes.
As can be seen in the sectional view of figure 1, such a diode is currently of a PNN type.
Figure 2 shows with a solid line the doping atom con-centration in such a diode.
Figure 3 shows, as a function of time, the ev~lution of the current in the diode and of the voltage at the term-inals of the diode during switching off.
As is shown by the long-dash curve in figure 2, when a forward current passes through this diode, a certain amount of charges is injected into the weakly doped N type zone.
This amount of injected charges or carriers depends on the current passing through the diode. The amount of charges ;
~ 32~7~
stored during forward conduction and remaining at time to of the switching cycle (figure 3) i9 generally designated by the symbol QO and is called stored charge. It i8 expressed by a relationship of the type :
QO ~ ~IF or QO ~ ~2 dIF/dt depending on the value of the duration to-t with respect to the value of ~ , where ~ is the life span of the minority carriers in the N type zone of the diode and where IF is the forward current in the diode.
When the voltage at the terminals of the circuit comp-rising the diode is reversed or when the current is derived from another part of the circuit, there is not found again immediately at the terminals of this diode a voltage having a value equal to that of the reverse voltage applied. On the 15 contrary, a certain time elapses during which the diode may be likened to a reverse short-circuit, before it reco~er~ its disabling power.
In fact, during switching, for a high-speed diode, a part of the charge QO disappears spontaneously by internal 20 recombination (related to the life-span of the minority carriers), but the other part, called recovered charge QR' which occurs essentially in the phenomenon studied is removed by the reverse current flowing through the diode. It is this recovered charge which produces the reverse recovery current 25 and induces all the switching phenomena (voltage surge, over-heating, parasites etc...).
The reverse recovery may be broken down into two parts (see also figure 3).
In a first part, from the time tf when the switch of 30 the switching circuit is closed, the forward current begins to decrease, is cancelled out and a reverse current irr is established. The rate of decrease of the forward current,and so the increase of the reverse current~is generally exclusively imposed by the circuit in which the diode is inserted.
Then frorn time t'l 5 the diode begins to recover its blocking power : the approaches to the junction become free of carriers (creation of adeplet~nzone or space charge zone), :
.
3 ~3~
a voltage is established at the terminals of the diode and the reverse current increases less quickly. At time tl, the reverse voltage applied is again found in its entirety at the terminals of the diode and the reverse current is at its 5 maximum. Between tO and tl, a charge amount Ql is removed.
There remains to be removed a charge ~2 corresponding to the hatched zone in figure 3 while the reverse current decreases and is cancelled out.
Finally, after time t2, since the current variation is 10 zero, there only remains at the terminals of the diode the reverse voltage applied.
To define the operation more exactly, it is advisable to examine to which physical parameters the charges Ql and Q2 correspond. We will consider the trend of the depletion zone 15 or space charge zone in the diode in two particular cases.
In figure 2, there is shown~with closely spaced dashes,curves EA and EB showing the distribution of the electric field when the diode is in the disabled state. In the case of curve EA, the thickness of the N zone is greater than the 20 width WE o~ thedepletionzone. In the case of curve EB, the depletion zoneextends over the whole thickness of the N layer.
During the period extending between times to and tl, all the injected carriers are eliminated which are present in the region in which the space charge zone is developed.
25 In the case of curve EA (N layer thick with respect to the extent of the deple~ionzone) injected carriers will remain after this first phase and charge Q2 corresponds to carriers which were present in the hatched zone of figure 2. In the case of curve EB, charge ~2 is practically zero and consequ-30 ently the period extending between times tl and t~ is very brief : the reverse current passes very quickly from its maximum amplitude IRM to a zero value~ This very rapid vari-ation of the current results in the creation of sonsiderable voltage surges VRM.
To construct in practice a high-speed diode in which the space charge has the configuration shown by curve EA, the reverse voltage to be obtained is taken as starting point.
.
4 gL~3~3t74 This determines the resistivity of ths N silicon to be used.
With this data acquired, the e~tent of the space charge WE
is calculated and the thickness WN of the N layer is chosen greater than WE. Finally, the life-span ~of the minority 5 carriers is reduced (gold, platinum diffusion ; electron bombardment ...) ; it is in fact this physical data which, for given conditions IF and dIF/dt, controls the amount of charges Q0 stored and, therefore, the switching speed of the diode (tl-to, t2-to, IRM). The life-span cannot be reduced 10 ad lib. So that the diode keeps correct characteristics in the conduct~gstate (characteristic VF = f(IF)),the life-span must be maintained above a minimum value which depends essentially on the thickness WN of the central N layer and whose minimum value is proportional to WN2. The charge 15 Q0 ~ ~IF and so the recovery time of the diode cannot then be reduced beyond a certain threshold.
Thus, to reduce Q0, the life-span and so the thickness of the N layer of the diode must be able to be reduced so as to have a configuration corresponding to curve EB in figure 20 2. A the present time, for the same reverse voltage behavior, a much higher silicon resistivity is used. Under a reverse voltage, the decrease of the field from the junction will be slow (curve EB) and the thickness WN of the N layer is deter-mined so as to obtain the desired voltage behavior. This 25 thickness may be reduced in a ratio practically equal to 2 with respect to the preceding case. This will then allow the life-span to be reduced to a considerably lower level (in principle 4 timeslower) and so much higher speed diodes to be obtained for which the value of IRM is much smaller than 30 in the preceding caseO But, as we have seen, the drawback is that the charge Q2 is then very small and that high voltage ; surges occur on switching.
It is one of the principal objects of the present invention to provide a diode ~hich, on the one hand, is ; ~ 35 extremely rapid and~ on the other, has a low voltage surge ~ during switching.
, . :
.
~L~3~g'7~L
SUMMARY OF THE INVENTION
To attain these objects as well as others, the present invention provides a PNN+ diode with high-speed switching off comprising, on an N~ type substrate with 5 high doping level, a first N type layer formed by low doping level epitaxy in which the life-span of the c~rriers is greatly reduced and a P type layer with high doping level, and further comprising a second N type epitaxied layer bet-ween the substrate and the first layer and whose impurity 10 concentration, intermediate between that of the substrate and that of the first layer, is less than the density of the free carriers injected into this second layer during the nominal forward current conduction phase just before switch-ing, the thickness of this second layer being such that, for 15 the nominal operating voltage in the blocking state, the de~letion zone reaches this layer without it however being completely depleted.
BRIEF DESCRIPTION OF THE DRAWINGS
The characteristics and advantages oF the present 20 invention will be set forth in detail in the following description of particular embodiments made with reference to i the accompanying figures in which :
Figures 1 to 3 have already been described for recall-ing the state of the art, Figure 4 is a schematic sectional view of a diode according to the present invention, Figure 5 shows different characteristic curves of the structure and of the operation of a diode of the invention, and Figures 6A and 6B shows respectively the variation of the current and of the voltage during blocking for a diode of the present invention compared with conventional diodes.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure ~ is a very schematical sectional view of a ~5 diode according to the present invention. This diode is form-ed from an N~ type substrate lû and comprises the convention-al N type layer 11 and P~ type layer 12. In addition, this ~,~
::
:`
1~3~
diode comprises an intermediate N, called Nl, type layer 13 between the N~ type substrate 10 and the weakly doped N type layer 11. As is conventional, layers 10 and 12, respectively of N and P+ type, have doping levels as high as possible, 5 greater than 1018 atoms/cm3. Layer 11, practically intrinsic, has a doping level of the order of 1013 to some 1014 atoms/
cm3. In a current configuration, the N layer has a doping level of the order of some 1014 to lDl~ atoms/cm3, but it will be seen that this doping level depends on the nominal 10 operating characteristics of the diode. The N and Nl layers are preferably formed by successive epitaxies on the N+ sub-strate. The P+ layer is for examplP formed by diffusion in the N layer.
Figure 5 shows with a solid line the variation of dopant 15 concentration in the diode as a function of the thickness.
With long dashes has been shown the excess free carrier concentration at time to in the switching cycle. This carrier amount depends on the nominal current in the diode and/or on the switching speed imposed by the circuit.
The curve, formed by closely spaced dashes, shows the distribution of the electric field when the diode is in the blocked state, WE designating the extent of thedePletionzone when the diode is in the blocked state for the nominal volt-age which it is intended to withstand.
Taking up again the notations of figure 3, during switching o~f of the diode between times to and tl, the injected carriers present in the zone which will be depleted at time tl are eliminated, and it is a part of the carriers situated in the hatched zone of figure 5 which will correspond to the 30 charge Q2 removed between times tl and t2.
According to the invention, it is essential for the number of these carriers to be sufficient so that the trans-ition between times tl and t2 is not too short so as not to cause too high a voltage surge VRM.
To adjust the time elapsing between times tl and t2, in accordance with the present invention the thickness and doping level of the Nl layer are varied. This doping level, ~' :j ~23~
intermediate betwPen the doping levels of the N and N+ layers, will be less than the charge density injected during the forward conduction.
Figures 6A and 6B reproduce oscillogra~ obtained 5 by the Applicant and illustrating the operation of diodes of the present invention with respect to diodes of the prior art.
Curves 20, 30, 40 show the variations of the current I
as a function of time and curves 21, 31, 41 the variations of lO the voltage V as a function of time at the terminals of a diode in the case of a high-speed "thick" diode, of a very high-speed diode of the prior art and of a diode according to the present invention, respectively.
Curves 20 and 21 correspond to the case of a high-speed 15 conventional diode in which the thickness WN of the N layer is greater than the extent WE of the space charge zone :
charge ql is high and therefore IRM has a high value and charge Q2 is sufficient for there to be no voltage oscillat-ion.
Curves 30 and 31 show what happens in the case of a diode such as shown in figures 1 and 2 when the thickness WN
of the N zone becomes less than the extent which the space charge zone would normally occupy in a zone of this type.
During disabling, since the charge Ql is low9 IRM is consid-25 erably less than its preceding value, but high voltage surges and current and voltage oscillations occur because of the very low value of the charge Q2 In accordance with the present invention, and as shown : by curves 40 and 41, these voltage surges are avoided with a 3n diode comprising an additional epitaxied layer Nl. The diode : of the present invention combines the advantages of these two types of high-speed diodes of the prior art : low value of tl-to and of IRM and limitation of the voltage surges and overoscillations. ~y carrying out tests, for nominal operat-35 ing voltage and current of the diode, as well as for a cut-off speed dIF/dt greater than a given threshold, a man skill-ed in the art will be able to determine the thickness and the ~ `
~ ~, ;` ``' . , .
~3L23~374 doping level of the epitaxied N1 layer as a function of the tolerated voltage surge level.
By way of example, oscillograms corresponding to curves 40 and 41, for which the current in the enabled state 5 was 30A and the reverse voltage ~00 volts, dIF/dt being 200A/microsecond, were obtained for a diode having a junction area of 0.3 cm with the following characteristics :
- P+ layer : surface concentration Cs-1.5 102at/cm3 9 thickness 20 microns 10 - N layer : thickness WN = 25 microns resistivity 35 ohms.cm (1.4 1014at~cm3) - Nl layer : thickness WNl = 15 microns 14 3 resistivity 5 ohms.cm (9.6 10 at/cm ), the life-span having been reduced by gold diffusion at 93SC.
Similarly, in the case of a current in theconducting state of 90A and a reverse voltage of 10~0 volts, dIF/dt 2 being equal to 90A/microsecond 9 a diode of an area of 0.3 cm may be constructed with the following parameters :
_ P~ layer : C5 = 1.5 102 at/cm3, thickness : 20microns 20 - N layer : WN = 60 microns resistivity 60 ohms.cm (1.8 1013 at/cm3) ~- Nl layer : WNl = 15 microns ; resistivity 2 ohms.cm (1.5 1015 at/cm3) the life-span being reduced by gold diffusion at 910C.
The present invention is not limited to the previously described e~bodiments, it covers on the contrary the differ-ent variations and generalizations included in the scope o~
the following claims. For example, the Nl layer, instead of having a constant concentration may have a variable impurity 30 concentration, weaker on the N layer side and stronger on the N+ substrate side. Thus, this concentration may vary continuously or in steps from the value of the concentration in the N layer to a hi~her value corresponding to orders of size of concentration indicated above.
~.
]
BACKGROUND ~F THE INVENTION
The present invention relates to a high speed diode capable for example of providing a rectifying or free-wheel diode function in a chopper circuit.
More particularly, ~he invention provides such a diode having improved characteristics during switching from the conducting to the ~locking state, that is to say a better switching off characteristic.
Although this aspPct i6 not developed herea it should be noted generally that a diode having good switching off characteristics also has better switching on characteristics.
To give a better understanding of the present invention, the principal parameters characterizing the switching off of a diode will first of all be ~efined. Certain theoretical explanations will also be recalled concerning the physical phenomena occurring during switching off. Nevertheless, even if the present theories prove to be wrong, the diode of the invention is defined by its structural characteristics and an error in the theoretical explanations could have no influence on the present invention whose advantages have been proved experimentally.
Figures 1, 2 and 3 characterize conven~ional high-speed diodes.
As can be seen in the sectional view of figure 1, such a diode is currently of a PNN type.
Figure 2 shows with a solid line the doping atom con-centration in such a diode.
Figure 3 shows, as a function of time, the ev~lution of the current in the diode and of the voltage at the term-inals of the diode during switching off.
As is shown by the long-dash curve in figure 2, when a forward current passes through this diode, a certain amount of charges is injected into the weakly doped N type zone.
This amount of injected charges or carriers depends on the current passing through the diode. The amount of charges ;
~ 32~7~
stored during forward conduction and remaining at time to of the switching cycle (figure 3) i9 generally designated by the symbol QO and is called stored charge. It i8 expressed by a relationship of the type :
QO ~ ~IF or QO ~ ~2 dIF/dt depending on the value of the duration to-t with respect to the value of ~ , where ~ is the life span of the minority carriers in the N type zone of the diode and where IF is the forward current in the diode.
When the voltage at the terminals of the circuit comp-rising the diode is reversed or when the current is derived from another part of the circuit, there is not found again immediately at the terminals of this diode a voltage having a value equal to that of the reverse voltage applied. On the 15 contrary, a certain time elapses during which the diode may be likened to a reverse short-circuit, before it reco~er~ its disabling power.
In fact, during switching, for a high-speed diode, a part of the charge QO disappears spontaneously by internal 20 recombination (related to the life-span of the minority carriers), but the other part, called recovered charge QR' which occurs essentially in the phenomenon studied is removed by the reverse current flowing through the diode. It is this recovered charge which produces the reverse recovery current 25 and induces all the switching phenomena (voltage surge, over-heating, parasites etc...).
The reverse recovery may be broken down into two parts (see also figure 3).
In a first part, from the time tf when the switch of 30 the switching circuit is closed, the forward current begins to decrease, is cancelled out and a reverse current irr is established. The rate of decrease of the forward current,and so the increase of the reverse current~is generally exclusively imposed by the circuit in which the diode is inserted.
Then frorn time t'l 5 the diode begins to recover its blocking power : the approaches to the junction become free of carriers (creation of adeplet~nzone or space charge zone), :
.
3 ~3~
a voltage is established at the terminals of the diode and the reverse current increases less quickly. At time tl, the reverse voltage applied is again found in its entirety at the terminals of the diode and the reverse current is at its 5 maximum. Between tO and tl, a charge amount Ql is removed.
There remains to be removed a charge ~2 corresponding to the hatched zone in figure 3 while the reverse current decreases and is cancelled out.
Finally, after time t2, since the current variation is 10 zero, there only remains at the terminals of the diode the reverse voltage applied.
To define the operation more exactly, it is advisable to examine to which physical parameters the charges Ql and Q2 correspond. We will consider the trend of the depletion zone 15 or space charge zone in the diode in two particular cases.
In figure 2, there is shown~with closely spaced dashes,curves EA and EB showing the distribution of the electric field when the diode is in the disabled state. In the case of curve EA, the thickness of the N zone is greater than the 20 width WE o~ thedepletionzone. In the case of curve EB, the depletion zoneextends over the whole thickness of the N layer.
During the period extending between times to and tl, all the injected carriers are eliminated which are present in the region in which the space charge zone is developed.
25 In the case of curve EA (N layer thick with respect to the extent of the deple~ionzone) injected carriers will remain after this first phase and charge Q2 corresponds to carriers which were present in the hatched zone of figure 2. In the case of curve EB, charge ~2 is practically zero and consequ-30 ently the period extending between times tl and t~ is very brief : the reverse current passes very quickly from its maximum amplitude IRM to a zero value~ This very rapid vari-ation of the current results in the creation of sonsiderable voltage surges VRM.
To construct in practice a high-speed diode in which the space charge has the configuration shown by curve EA, the reverse voltage to be obtained is taken as starting point.
.
4 gL~3~3t74 This determines the resistivity of ths N silicon to be used.
With this data acquired, the e~tent of the space charge WE
is calculated and the thickness WN of the N layer is chosen greater than WE. Finally, the life-span ~of the minority 5 carriers is reduced (gold, platinum diffusion ; electron bombardment ...) ; it is in fact this physical data which, for given conditions IF and dIF/dt, controls the amount of charges Q0 stored and, therefore, the switching speed of the diode (tl-to, t2-to, IRM). The life-span cannot be reduced 10 ad lib. So that the diode keeps correct characteristics in the conduct~gstate (characteristic VF = f(IF)),the life-span must be maintained above a minimum value which depends essentially on the thickness WN of the central N layer and whose minimum value is proportional to WN2. The charge 15 Q0 ~ ~IF and so the recovery time of the diode cannot then be reduced beyond a certain threshold.
Thus, to reduce Q0, the life-span and so the thickness of the N layer of the diode must be able to be reduced so as to have a configuration corresponding to curve EB in figure 20 2. A the present time, for the same reverse voltage behavior, a much higher silicon resistivity is used. Under a reverse voltage, the decrease of the field from the junction will be slow (curve EB) and the thickness WN of the N layer is deter-mined so as to obtain the desired voltage behavior. This 25 thickness may be reduced in a ratio practically equal to 2 with respect to the preceding case. This will then allow the life-span to be reduced to a considerably lower level (in principle 4 timeslower) and so much higher speed diodes to be obtained for which the value of IRM is much smaller than 30 in the preceding caseO But, as we have seen, the drawback is that the charge Q2 is then very small and that high voltage ; surges occur on switching.
It is one of the principal objects of the present invention to provide a diode ~hich, on the one hand, is ; ~ 35 extremely rapid and~ on the other, has a low voltage surge ~ during switching.
, . :
.
~L~3~g'7~L
SUMMARY OF THE INVENTION
To attain these objects as well as others, the present invention provides a PNN+ diode with high-speed switching off comprising, on an N~ type substrate with 5 high doping level, a first N type layer formed by low doping level epitaxy in which the life-span of the c~rriers is greatly reduced and a P type layer with high doping level, and further comprising a second N type epitaxied layer bet-ween the substrate and the first layer and whose impurity 10 concentration, intermediate between that of the substrate and that of the first layer, is less than the density of the free carriers injected into this second layer during the nominal forward current conduction phase just before switch-ing, the thickness of this second layer being such that, for 15 the nominal operating voltage in the blocking state, the de~letion zone reaches this layer without it however being completely depleted.
BRIEF DESCRIPTION OF THE DRAWINGS
The characteristics and advantages oF the present 20 invention will be set forth in detail in the following description of particular embodiments made with reference to i the accompanying figures in which :
Figures 1 to 3 have already been described for recall-ing the state of the art, Figure 4 is a schematic sectional view of a diode according to the present invention, Figure 5 shows different characteristic curves of the structure and of the operation of a diode of the invention, and Figures 6A and 6B shows respectively the variation of the current and of the voltage during blocking for a diode of the present invention compared with conventional diodes.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure ~ is a very schematical sectional view of a ~5 diode according to the present invention. This diode is form-ed from an N~ type substrate lû and comprises the convention-al N type layer 11 and P~ type layer 12. In addition, this ~,~
::
:`
1~3~
diode comprises an intermediate N, called Nl, type layer 13 between the N~ type substrate 10 and the weakly doped N type layer 11. As is conventional, layers 10 and 12, respectively of N and P+ type, have doping levels as high as possible, 5 greater than 1018 atoms/cm3. Layer 11, practically intrinsic, has a doping level of the order of 1013 to some 1014 atoms/
cm3. In a current configuration, the N layer has a doping level of the order of some 1014 to lDl~ atoms/cm3, but it will be seen that this doping level depends on the nominal 10 operating characteristics of the diode. The N and Nl layers are preferably formed by successive epitaxies on the N+ sub-strate. The P+ layer is for examplP formed by diffusion in the N layer.
Figure 5 shows with a solid line the variation of dopant 15 concentration in the diode as a function of the thickness.
With long dashes has been shown the excess free carrier concentration at time to in the switching cycle. This carrier amount depends on the nominal current in the diode and/or on the switching speed imposed by the circuit.
The curve, formed by closely spaced dashes, shows the distribution of the electric field when the diode is in the blocked state, WE designating the extent of thedePletionzone when the diode is in the blocked state for the nominal volt-age which it is intended to withstand.
Taking up again the notations of figure 3, during switching o~f of the diode between times to and tl, the injected carriers present in the zone which will be depleted at time tl are eliminated, and it is a part of the carriers situated in the hatched zone of figure 5 which will correspond to the 30 charge Q2 removed between times tl and t2.
According to the invention, it is essential for the number of these carriers to be sufficient so that the trans-ition between times tl and t2 is not too short so as not to cause too high a voltage surge VRM.
To adjust the time elapsing between times tl and t2, in accordance with the present invention the thickness and doping level of the Nl layer are varied. This doping level, ~' :j ~23~
intermediate betwPen the doping levels of the N and N+ layers, will be less than the charge density injected during the forward conduction.
Figures 6A and 6B reproduce oscillogra~ obtained 5 by the Applicant and illustrating the operation of diodes of the present invention with respect to diodes of the prior art.
Curves 20, 30, 40 show the variations of the current I
as a function of time and curves 21, 31, 41 the variations of lO the voltage V as a function of time at the terminals of a diode in the case of a high-speed "thick" diode, of a very high-speed diode of the prior art and of a diode according to the present invention, respectively.
Curves 20 and 21 correspond to the case of a high-speed 15 conventional diode in which the thickness WN of the N layer is greater than the extent WE of the space charge zone :
charge ql is high and therefore IRM has a high value and charge Q2 is sufficient for there to be no voltage oscillat-ion.
Curves 30 and 31 show what happens in the case of a diode such as shown in figures 1 and 2 when the thickness WN
of the N zone becomes less than the extent which the space charge zone would normally occupy in a zone of this type.
During disabling, since the charge Ql is low9 IRM is consid-25 erably less than its preceding value, but high voltage surges and current and voltage oscillations occur because of the very low value of the charge Q2 In accordance with the present invention, and as shown : by curves 40 and 41, these voltage surges are avoided with a 3n diode comprising an additional epitaxied layer Nl. The diode : of the present invention combines the advantages of these two types of high-speed diodes of the prior art : low value of tl-to and of IRM and limitation of the voltage surges and overoscillations. ~y carrying out tests, for nominal operat-35 ing voltage and current of the diode, as well as for a cut-off speed dIF/dt greater than a given threshold, a man skill-ed in the art will be able to determine the thickness and the ~ `
~ ~, ;` ``' . , .
~3L23~374 doping level of the epitaxied N1 layer as a function of the tolerated voltage surge level.
By way of example, oscillograms corresponding to curves 40 and 41, for which the current in the enabled state 5 was 30A and the reverse voltage ~00 volts, dIF/dt being 200A/microsecond, were obtained for a diode having a junction area of 0.3 cm with the following characteristics :
- P+ layer : surface concentration Cs-1.5 102at/cm3 9 thickness 20 microns 10 - N layer : thickness WN = 25 microns resistivity 35 ohms.cm (1.4 1014at~cm3) - Nl layer : thickness WNl = 15 microns 14 3 resistivity 5 ohms.cm (9.6 10 at/cm ), the life-span having been reduced by gold diffusion at 93SC.
Similarly, in the case of a current in theconducting state of 90A and a reverse voltage of 10~0 volts, dIF/dt 2 being equal to 90A/microsecond 9 a diode of an area of 0.3 cm may be constructed with the following parameters :
_ P~ layer : C5 = 1.5 102 at/cm3, thickness : 20microns 20 - N layer : WN = 60 microns resistivity 60 ohms.cm (1.8 1013 at/cm3) ~- Nl layer : WNl = 15 microns ; resistivity 2 ohms.cm (1.5 1015 at/cm3) the life-span being reduced by gold diffusion at 910C.
The present invention is not limited to the previously described e~bodiments, it covers on the contrary the differ-ent variations and generalizations included in the scope o~
the following claims. For example, the Nl layer, instead of having a constant concentration may have a variable impurity 30 concentration, weaker on the N layer side and stronger on the N+ substrate side. Thus, this concentration may vary continuously or in steps from the value of the concentration in the N layer to a hi~her value corresponding to orders of size of concentration indicated above.
~.
Claims (7)
1. In a PNN+ diode with high speed switching off, comprising on an N+ type substrate with high doping level a first N type layer with low doping level in which the life-span of the carriers is greatly reduced and a P
type layer with high doping level, there is further provided a second N type layer (N1 layer) between said substrate and said first layer and in which the impurity concentration is intermediate between that of said substrate and that of said first layer, the thickness of this second layer being such that, for the nominal operating voltage in theblocking state, thedepletionzone reaches this layer without it however being completely depleted.
type layer with high doping level, there is further provided a second N type layer (N1 layer) between said substrate and said first layer and in which the impurity concentration is intermediate between that of said substrate and that of said first layer, the thickness of this second layer being such that, for the nominal operating voltage in theblocking state, thedepletionzone reaches this layer without it however being completely depleted.
2. The diode as claimed in claim 1, wherein said second and first layers are formed by successive epitaxies.
3. The PNN+ diode as claimed in claim 1, wherein the life-span of the carriers in said first N type layer is reduced by gold or platinum diffusion.
4. The PNN+ diode as claimed in claim 1, wherein the impurity concentration of said second N1 layer is less than the density of the free carriers in excess at the time of switching for the nominal operating conditions of the diode (nominal current, cut-off speed of this current).
5. The PNN+ diode as claimed in claim 1, wherein said first N layer has a doping level of the order of 1013 to some 1014 atoms/cm3 and said second N1 layer of the order of some 1014 to 1016 atoms/cm3.
6. The PNN+ diode as claimed in claim 1, wherein said second N1 layer has a thickness of the order of 10 to 50 microns;
7. The PNN diode as claimed in claim 1, wherein the concentration of said second N1 layer is not constant over the thickness of this layer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8205435A FR2524715A1 (en) | 1982-03-30 | 1982-03-30 | FAST DIODE |
| FR8205435 | 1982-03-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1232974A true CA1232974A (en) | 1988-02-16 |
Family
ID=9272559
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000424725A Expired CA1232974A (en) | 1982-03-30 | 1983-03-29 | High speed diode |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0090722B1 (en) |
| JP (1) | JPS58182277A (en) |
| CA (1) | CA1232974A (en) |
| DE (1) | DE3361323D1 (en) |
| FR (1) | FR2524715A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5773858A (en) * | 1992-01-17 | 1998-06-30 | Eupec Europaeische Gesellschaft Fuer Leistungshalbleiter Mbh & Co. Kg. | Power diode |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5929469A (en) * | 1982-08-11 | 1984-02-16 | Hitachi Ltd | Semiconductor device |
| FR2556882B1 (en) * | 1983-12-14 | 1986-05-23 | Fairchild Camera Instr Co | FAST SEMICONDUCTOR COMPONENT, ESPECIALLY HIGH VOLTAGE PIN DIODE |
| DE3633161A1 (en) * | 1986-09-30 | 1988-04-07 | Licentia Gmbh | SEMICONDUCTOR COMPONENT WITH AN ANODE-SIDED P-ZONE AND A LOW-DOPED N-BASE ZONE |
| FR2638892B1 (en) * | 1988-11-09 | 1992-12-24 | Sgs Thomson Microelectronics | METHOD FOR MODULATING THE QUANTITY OF GOLD DIFFUSED IN A SILICON SUBSTRATE AND RAPID DIODE OBTAINED BY THIS PROCESS |
| JPH06314801A (en) * | 1993-03-05 | 1994-11-08 | Mitsubishi Electric Corp | Semiconductor device and manufacture thereof |
| JP4364945B2 (en) * | 1996-10-14 | 2009-11-18 | クリー、インコーポレイテッド | Bipolar semiconductor device manufacturing method |
| DE10344609B3 (en) | 2003-09-25 | 2005-07-21 | Infineon Technologies Ag | RF diode |
| JP5135666B2 (en) * | 2005-04-14 | 2013-02-06 | 株式会社日立製作所 | Power converter |
| JP2007184439A (en) * | 2006-01-10 | 2007-07-19 | Shindengen Electric Mfg Co Ltd | Semiconductor device |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1576940A (en) * | 1968-08-13 | 1969-08-01 | ||
| US3553536A (en) * | 1968-11-19 | 1971-01-05 | Rca Corp | Semiconductor rectifiers having controlled storage and recovery characteristics |
| US3727116A (en) * | 1970-05-05 | 1973-04-10 | Rca Corp | Integral thyristor-rectifier device |
| US3710203A (en) * | 1971-11-05 | 1973-01-09 | Fmc Corp | High power storage diode |
| DE2608432C3 (en) * | 1976-03-01 | 1981-07-09 | Siemens AG, 1000 Berlin und 8000 München | Power diode |
| FR2347781A1 (en) * | 1976-04-08 | 1977-11-04 | Alsthom Cgee | REVERSE CONDUCTION THYRISTOR |
-
1982
- 1982-03-30 FR FR8205435A patent/FR2524715A1/en active Granted
-
1983
- 1983-03-22 EP EP83400591A patent/EP0090722B1/en not_active Expired
- 1983-03-22 DE DE8383400591T patent/DE3361323D1/en not_active Expired
- 1983-03-29 CA CA000424725A patent/CA1232974A/en not_active Expired
- 1983-03-29 JP JP5347183A patent/JPS58182277A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5773858A (en) * | 1992-01-17 | 1998-06-30 | Eupec Europaeische Gesellschaft Fuer Leistungshalbleiter Mbh & Co. Kg. | Power diode |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0090722A1 (en) | 1983-10-05 |
| FR2524715B1 (en) | 1984-05-18 |
| JPS58182277A (en) | 1983-10-25 |
| DE3361323D1 (en) | 1986-01-09 |
| FR2524715A1 (en) | 1983-10-07 |
| EP0090722B1 (en) | 1985-11-27 |
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