A Novel Concept of Electron–Hole Enhancement for Superjunction Reverse-Conducting Insulated Gate Bipolar Transistor with Electron-Blocking Layer

A novel snapback-free superjunction reverse-conducting insulated gate bipolar transistor (SJ-RC-IGBT) is proposed and verified by simulation. In the SJ-RC-IGBT, the parasitic P/N/P/N structure as thyristor or Shockley diode demonstrates large conductivity due to an overabundance of carriers for reverse conduction. By preventing electrons from leaking across the N+ region at the collector side, the extra electron-blocking (EB) layer introduced in the SJ-RC-IGBT can dramatically enhance electron–hole pairs in the N/P-pillars. Hence, the SJ-RC-IGBT demonstrates a low on-state voltage (Von). In addition, snapback-free characteristics and a large safe operating area (SOA) are also achieved in the SJ-RC-IGBT. During the turn-off process, a significant amount of electrons are extracted by parasitic MOS across the EB layer at the collector side to decrease the turn-off loss (Eoff). According to the optimized results, the SJ-RC-IGBT with EB layer obtains an ultralow Eoff of 3.9 mJ/cm2 at Von = 1.38 V with 88% and 81% decreases, respectively, compared with the conventional reverse-conducting IGBT (CRC-IGBT) and superjunction IGBT (SJ-IGBT).


Introduction
The reverse-conducting insulated gate bipolar transistor (RC-IGBT) is a crucial component for packing in a single power module at a low package cost, and it plays vital roles in medium and high voltage inverters [1,2]. The RC-IGBT works in a forward and reverse state, necessitating [3][4][5][6]: (i) reverse conduction with a uniform current distribution; (ii) forward conduction with the lowest possible on-state voltage (V on ) and without a snapback effect at the high carrier injection for conductive modulation; (iii) high-speed switching for the lowest possible turn-off power dissipation by accelerating carrier extraction. It is well known that the conventional RC-IGBT (CRC-IGBT) is achieved by anti-paralleling to a freewheeling diode (FWD) as an anode-short IGBT for reverse conduction. However, the CRC-IGBT easily results in a snapback phenomenon and a relatively high V on at forward conduction and non-uniform current distribution at reverse conduction [3], which are, however, in conflict with the design requirements. The reverse-conducting capability and the snapback-free are desirable pursuits of the RC-IGBT design [7]. Although the snapback-free can be achieved by these techniques, such as a floating p-region in the trench collector [8] and discontinuous field-stop (FS) layer [9], these RC-IGBTs are at the expense of V on and the forward conducting uniformity compared with conventional IGBTs. Therefore, in the RC-IGBT, an anti-parallel thyristor [10] or a Shockley diode [11] are introduced other than a FWD in the CRC-IGBT to realize both reverse conduction and suppress the snapback effect, which easily causes reverse snapback [7]. Moreover, the issue of current crowding is another challenge for obtaining a large safe operating area (SOA) in these RC-IGBTs. To eliminate the current-crowding problem, the edge-termination concept [12] Figure 1a-c show the schematic views of the SJ-RC-IGBT, SJ-IGBT and CRC-IGBT, respectively. The dimensions are shown in the figure. If it has no special specification, the key doping concentrations are N pillar = 3 × 10 15 cm −3 -doping concentration of the N/P-pillars, N CS = 1 × 10 16 cm −3 -doping concentration of the CS layer, and N FS = 2 × 10 16 cm −3 -doping concentration of the FS layer. In the SJ-RC-IGBT, the doping concentration of the EB layer (N EB ) is 2 × 10 16 cm −3 . In the CRC-IGBT, the doping concentration of N-drift (N d ) is 1 × 10 13 cm −3 . Two-dimensional simulator MEDICI have been carried out, and the physical models-CONMOB (carrier mobility model dependence on doping concentration), FLDMOB (carrier mobility model dependence on high electric field), SRFMOB2 (enhanced surface mobility model), CONSRH (Shockley-Read-Hall recombination model), AUGER (Auger recombination model), BGN (Slotboom bandgap narrowing model), and IMPACT.I (impact ionization model)-are included [22]. The simulation is verified with data and calibrated [23]. The carrier lifetime (τ) is set at 1 µs [24]. If it has no special specification, the key doping concentrations are Npillar = 3 × 10 15 cm −3 -doping concentration of the N/Ppillars, NCS = 1 × 10 16 cm −3 -doping concentration of the CS layer, and NFS = 2 × 10 16 cm −3doping concentration of the FS layer. In the SJ-RC-IGBT, the doping concentration of the EB layer (NEB) is 2 × 10 16 cm −3 . In the CRC-IGBT, the doping concentration of N-drift (Nd) is 1 × 10 13 cm −3 . Two-dimensional simulator MEDICI have been carried out, and the physical models-CONMOB (carrier mobility model dependence on doping concentration), FLDMOB (carrier mobility model dependence on high electric field), SRFMOB2 (enhanced surface mobility model), CONSRH (Shockley-Read-Hall recombination model), AUGER (Auger recombination model), BGN (Slotboom bandgap narrowing model), and IMPACT.I (impact ionization model)-are included [22]. The simulation is verified with data and calibrated [23]. The carrier lifetime (τ) is set at 1 µs [24].  Compared with the SJ-IGBT and CRC-IGBT, the main feature is that an EB layer at the bottom of the P-pillar and an additional trench collector inserted into the N-pillar and P-pillar to separate the N+/P+ collector regions are implanted in the SJ-RC-IGBT. At the emitter side, the injected holes in the N/P-pillars are blocked by the CS layer, and at the collector side, the injected electrons are blocked by the EB layer. Therefore, electron-hole pairs in the N/P-pillars are further improved by the CS layer and EB layer higher than the SJ-RC-IGBT without the EB layer. In the SJ-RC-IGBT, the EB layer and CS layer help the reduction of Von. During the turn-off process, the trench collector can speed up extraction of the excess carriers from the N/P-pillars for a low Eoff. Otherwise, if the CS layer is introduced in the SJ-IGBT, the optimization of the Von-Eoff trade-off is also achieved but without the reverse-conducting capability, as given in [22].

Emitter
In order to illustrate the carrier-storage effect of the EB layer and CS layer, Figure 2a shows the schematic energy-band views and carrier distributions at VG = 15 V and VCE = 1 V. The doping concentration of the EB layer increasing from 1.0 × 10 16 cm −3 to 2.0 × 10 16 cm −3 can enhance the electron concentration along line BB' from ~1.5 × 10 15 cm −3 to ~5.8 × 10 15 cm −3 in the P-pillar and from ~5.5 × 10 15 cm −3 to ~9.8 × 10 15 cm −3 in the N-pillar, as shown in Figure 2b. The structure without the EB layer means that the corresponding region is filled by the P-pillar. It is obviously found that the EB layer as electron barrier can enhance the carrier-storage effect in the N/P-pillars, but in the absence of the EB layer, the holestorage effect by the CS layer is weakened. Compared with the SJ-IGBT and CRC-IGBT, the main feature is that an EB layer at the bottom of the P-pillar and an additional trench collector inserted into the N-pillar and P-pillar to separate the N+/P+ collector regions are implanted in the SJ-RC-IGBT. At the emitter side, the injected holes in the N/P-pillars are blocked by the CS layer, and at the collector side, the injected electrons are blocked by the EB layer. Therefore, electron-hole pairs in the N/P-pillars are further improved by the CS layer and EB layer higher than the SJ-RC-IGBT without the EB layer. In the SJ-RC-IGBT, the EB layer and CS layer help the reduction of V on . During the turn-off process, the trench collector can speed up extraction of the excess carriers from the N/P-pillars for a low E off . Otherwise, if the CS layer is introduced in the SJ-IGBT, the optimization of the V on -E off trade-off is also achieved but without the reverse-conducting capability, as given in [22].
In order to illustrate the carrier-storage effect of the EB layer and CS layer, Figure 2a shows the schematic energy-band views and carrier distributions at V G = 15 V and V CE = 1 V. The doping concentration of the EB layer increasing from 1.0 × 10 16 cm −3 to 2.0 × 10 16 cm −3 can enhance the electron concentration along line BB' from~1.5 × 10 15 cm −3 to~5.8 × 10 15 cm −3 in the P-pillar and from~5.5 × 10 15 cm −3 to~9.8 × 10 15 cm −3 in the N-pillar, as shown in Figure 2b. The structure without the EB layer means that the corresponding region is filled by the P-pillar. It is obviously found that the EB layer as electron barrier can enhance the carrier-storage effect in the N/P-pillars, but in the absence of the EB layer, the hole-storage effect by the CS layer is weakened.        At reverse conduction, holes are injected from the P+ region at the emitter side into the N/P-pillars and electrons are injected from the N+ region at the collector side, as shown in Figure 3a. In the beginning, BJTs B7 and B8 are turned on as the first thyristor, then BJTs B6 and B11 are turned on as the second thyristor. With an increase of the reverse current, the voltage drop across the junction of the P-body/CS layer is larger than ~0.7 V, with BJTs B9 and B10 triggered on. At last, BJT B5 is turned on by the effective base current at a positive biased emitter. The equivalent circuit of the SJ-RC-IGBT at reverse conduction is illustrated in Figure 3b.

Reverse-and Forward-Conducting Mechanism
Figure 3c-f show the distributions of current at reverse conduction. At 10 mA/cm 2 , holes are injected from the emitter region and electrons are injected from the collector region of the SJ-RC-IGBT as two serial P/N junctions. Because of the narrow CS layer, BJTs B7 and B8 work as a thyristor with a low voltage drop. With an increase of reverse bias of the emitter, the conduction current is increased from 40 mA/cm 2 to 70 mA/cm 2 for BJTs B6, B9, B10, and B11 on and from 70 mA/cm 2 to 500 mA/cm 2 for BJT B5 on. Eventually, at a high reverse current condition, the N/P-pillars become high conductivity regions.
At forward conduction, the parasitic MOSFETs (M1, M2, and M3) around the gate are firstly turned on. Electrons from the N+ emitter region and holes from the P+ collector region are injected into the N/P-pillars, as shown in Figure 4a. The forward equivalent circuit is illustrated in Figure 4b. The injected electrons into the N-pillar trigger on BJTs B1 and B2. With the forward current increasing, the junction of the P-pillar/CS layer will be forward biased sufficiently large enough to inject minority carriers from the P-pillar to the CS layer, and then BJT B4 is triggered on. Since the base region of BJT B4 is formed by a narrow CS layer with a relatively high doping concentration, BJT B4 works as a low gain BJT. As forward conduction increases, the junction of the P-pillar/CS layer is further positively biased. The parasitic BJT B3 is turned on. There is a weak conduction channel for electrons in M4 (parasitic MOSFET around the trench collector) to offer a path for electron extraction when the SJ-RC-IGBT is turned off.
Figure 4c-f show the distributions of current at forward conduction. At low forward conduction (10 mA/cm 2 ), electrons injected from MOSFET M2 as unipolar current is intended for the base of BJT B1. Up to 50 mA/cm 2 , holes injected from the P+ collector region and electrons injected from MOSFETs M3 and M1 can activate BJTs B1 and B2. When the conduction current increases to 100 mA/cm 2 , BJT B4 works at on-state. At last, the N+ collector region potential is high enough for triggering BJT B3 on at 500 mA/cm 2 . There are At reverse conduction, holes are injected from the P+ region at the emitter side into the N/P-pillars and electrons are injected from the N+ region at the collector side, as shown in Figure 3a. In the beginning, BJTs B 7 and B 8 are turned on as the first thyristor, then BJTs B 6 and B 11 are turned on as the second thyristor. With an increase of the reverse current, the voltage drop across the junction of the P-body/CS layer is larger than~0.7 V, with BJTs B 9 and B 10 triggered on. At last, BJT B 5 is turned on by the effective base current at a positive biased emitter. The equivalent circuit of the SJ-RC-IGBT at reverse conduction is illustrated in Figure 3b.
Figure 3c-f show the distributions of current at reverse conduction. At 10 mA/cm 2 , holes are injected from the emitter region and electrons are injected from the collector region of the SJ-RC-IGBT as two serial P/N junctions. Because of the narrow CS layer, BJTs B 7 and B 8 work as a thyristor with a low voltage drop. With an increase of reverse bias of the emitter, the conduction current is increased from 40 mA/cm 2 to 70 mA/cm 2 for BJTs B 6 , B 9 , B 10 , and B 11 on and from 70 mA/cm 2 to 500 mA/cm 2 for BJT B 5 on. Eventually, at a high reverse current condition, the N/P-pillars become high conductivity regions.
At forward conduction, the parasitic MOSFETs (M 1 , M 2 , and M 3 ) around the gate are firstly turned on. Electrons from the N+ emitter region and holes from the P+ collector region are injected into the N/P-pillars, as shown in Figure 4a. The forward equivalent circuit is illustrated in Figure 4b. The injected electrons into the N-pillar trigger on BJTs B 1 and B 2 . With the forward current increasing, the junction of the P-pillar/CS layer will be forward biased sufficiently large enough to inject minority carriers from the P-pillar to the CS layer, and then BJT B 4 is triggered on. Since the base region of BJT B 4 is formed by a narrow CS layer with a relatively high doping concentration, BJT B 4 works as a low gain BJT. As forward conduction increases, the junction of the P-pillar/CS layer is further positively biased. The parasitic BJT B 3 is turned on. There is a weak conduction channel for electrons in M 4 (parasitic MOSFET around the trench collector) to offer a path for electron extraction when the SJ-RC-IGBT is turned off. Figure 4c-f show the distributions of current at forward conduction. At low forward conduction (10 mA/cm 2 ), electrons injected from MOSFET M 2 as unipolar current is intended for the base of BJT B 1 . Up to 50 mA/cm 2 , holes injected from the P+ collector region and electrons injected from MOSFETs M 3 and M 1 can activate BJTs B 1 and B 2 . When the conduction current increases to 100 mA/cm 2 , BJT B 4 works at on-state. At last, the N+ collector region potential is high enough for triggering BJT B 3 on at 500 mA/cm 2 . There are two conduction channels with a low barrier for electrons from MOSFET M 1 to MOSFET M 4 around the trench collector. Figure 5 shows the forward/reverse I-V curves of the SJ-RC-IGBT, SJ-IGBT, and CRC-IGBT. From Figure 5a, it is obviously found that the SJ-IGBT and SJ-RC-IGBT turn on with snapback-free, but the CRC-IGBT has a snapback phenomenon at L P = 170 µm and 200 µm. Due to the inhibition of unipolar conduction provided by the N+ collector area, the snapback effect in the CRC-IGBT can be fully removed when L P increases to 270 µm. As shown in the inset of Figure 5a, the forward conduction exceeds that of the SJ-IGBT after I CE of the SJ-RC-IGBT exceeds 33.1 A/cm 2 . The minimum voltage drop (1.24 V) at I CE = 100 A/cm 2 is also obtained in the SJ-RC-IGBT. Figure 5b shows the reverse I-V curves of the SJ-RC-IGBT and CRC-IGBT. Although the reverse voltage drop of the CRC-IGBT can be decreased with the reduction of L P , this is a contradiction as an elimination of the snapback phenomenon. However, the SJ-RC-IGBT demonstrates superior performance: a small reverse voltage drop and a uniform distribution of current. The thyristor is prone to snapback during the conduction process due to the positive feedback of the P/N/P/N structure needing some conditions, with the main factor being τ. The positive feedback cannot be formed if the τ is too small, as the thyristor will withstand voltage until the minority carriers can pass through the base region, then the snapback will occur. In [11], the RC-IGBT with Shockley diode (SH-RC-IGBT) has a snapback-free at a reverse voltage drop of 0.95 V. Further lowering the reverse voltage drop in SH-RC-IGBT makes it challenging to activate the parasitic thyristor without snapback. Hence, the RC-IGBT with Shockley diode (SH-RC-IGBT) has a snapback phenomenon even though it has the bigger τ with lower reverse voltage drop, as shown is Figure 5c, but it is snapback-free for the SJ-RC-IGBT. This is due to the electron being injected into the N-pillar through the boundary of the trench collector.

Conduction Characteristics
two conduction channels with a low barrier for electrons from MOSFET M1 to MOSFET M4 around the trench collector. Figure 5 shows the forward/reverse I-V curves of the SJ-RC-IGBT, SJ-IGBT, and CRC-IGBT. From Figure 5a, it is obviously found that the SJ-IGBT and SJ-RC-IGBT turn on with snapback-free, but the CRC-IGBT has a snapback phenomenon at LP = 170 µm and 200 µm. Due to the inhibition of unipolar conduction provided by the N+ collector area, the snapback effect in the CRC-IGBT can be fully removed when LP increases to 270 µm. As shown in the inset of Figure 5a, the forward conduction exceeds that of the SJ-IGBT after ICE of the SJ-RC-IGBT exceeds 33.1 A/cm 2 . The minimum voltage drop (1.24 V) at ICE = 100 A/cm 2 is also obtained in the SJ-RC-IGBT. Figure 5b shows the reverse I-V curves of the SJ-RC-IGBT and CRC-IGBT. Although the reverse voltage drop of the CRC-IGBT can be decreased with the reduction of LP, this is a contradiction as an elimination of the snapback phenomenon. However, the SJ-RC-IGBT demonstrates superior performance: a small reverse voltage drop and a uniform distribution of current. The thyristor is prone to snapback during the conduction process due to the positive feedback of the P/N/P/N structure needing some conditions, with the main factor being τ. The positive feedback cannot be formed if the τ is too small, as the thyristor will withstand voltage until the minority carriers can pass through the base region, then the snapback will occur. In [11], the RC-IGBT with Shockley diode (SH-RC-IGBT) has a snapback-free at a reverse voltage drop of 0.95 V. Further lowering the reverse voltage drop in SH-RC-IGBT makes it challenging to activate the parasitic thyristor without snapback. Hence, the RC-IGBT with Shockley diode (SH-RC-IGBT) has a snapback phenomenon even though it has the bigger τ with lower reverse voltage drop, as shown is Figure 5c, but it is snapback-free for the SJ-RC-IGBT. This is due to the electron being injected into the N-pillar through the boundary of the trench collector.

Safe Operating Area
Conventionally, the instability of the IGBT is prone to trigger on parasitic BJTs, giving rise to a non-uniform current distribution at quasi-saturation conduction and high voltage bias. As shown in Figure 6a, the I-V curves of the CRC-IGBT snapback below 800 V much lower than that of the SJ-IGBT, as shown in Figure 6b, and the SJ-RC-IGBT, as shown in Figure 6c. This is mainly because the non-uniform current regenerates high space charge modulation in the absence of a uniform electric field. In the SJ-IGBT and SJ-RC-IGBT, the N/P-pillars can offer a uniform conduction path without crowding space charges and avoiding immature breakdown. Although the saturation current density of the SJ-RC-IGBT is higher than the CRC-IGBT, the SOA of the SJ-RC-IGBT is continuously improved, due to uniform current regions sustained by the N/P-pillars.  Figure 7a shows the breakdown voltage (BV) versus NEB and NCS. In the range of NEB = 1.2 × 10 16 cm −3 -2.4 × 10 16 cm −3 , BV has a small variation at a certain NCS. Figure 7b shows

Safe Operating Area
Conventionally, the instability of the IGBT is prone to trigger on parasitic BJTs, giving rise to a non-uniform current distribution at quasi-saturation conduction and high voltage bias. As shown in Figure 6a, the I-V curves of the CRC-IGBT snapback below 800 V much lower than that of the SJ-IGBT, as shown in Figure 6b, and the SJ-RC-IGBT, as shown in Figure 6c. This is mainly because the non-uniform current regenerates high space charge modulation in the absence of a uniform electric field. In the SJ-IGBT and SJ-RC-IGBT, the N/P-pillars can offer a uniform conduction path without crowding space charges and avoiding immature breakdown. Although the saturation current density of the SJ-RC-IGBT is higher than the CRC-IGBT, the SOA of the SJ-RC-IGBT is continuously improved, due to uniform current regions sustained by the N/P-pillars.

Safe Operating Area
Conventionally, the instability of the IGBT is prone to trigger on parasitic BJTs, giving rise to a non-uniform current distribution at quasi-saturation conduction and high voltage bias. As shown in Figure 6a, the I-V curves of the CRC-IGBT snapback below 800 V much lower than that of the SJ-IGBT, as shown in Figure 6b, and the SJ-RC-IGBT, as shown in Figure 6c. This is mainly because the non-uniform current regenerates high space charge modulation in the absence of a uniform electric field. In the SJ-IGBT and SJ-RC-IGBT, the N/P-pillars can offer a uniform conduction path without crowding space charges and avoiding immature breakdown. Although the saturation current density of the SJ-RC-IGBT is higher than the CRC-IGBT, the SOA of the SJ-RC-IGBT is continuously improved, due to uniform current regions sustained by the N/P-pillars.  Figure 7a shows the breakdown voltage (BV) versus NEB and NCS. In the range of NEB = 1.2 × 10 16 cm −3 -2.4 × 10 16 cm −3 , BV has a small variation at a certain NCS. Figure 7b shows Von versus NEB and NCS. During forward conduction, Von is influenced by the ambipolar effect. The increase of NCS leads to a high hole potential barrier near the P-body to restrict hole extraction. Meanwhile, the increase of NEB results in raising the electron potential barrier to enhance hole injection in the N-pillar for achieving high conductive modulation. Hence, both an NCS and NEB increase can reduce Von.   Figure 7b shows V on versus N EB and N CS . During forward conduction, V on is influenced by the ambipolar effect. The increase of N CS leads to a high hole potential barrier near the P-body to restrict hole extraction. Meanwhile, the increase of N EB results in raising the electron potential barrier to enhance hole injection in the N-pillar for achieving high conductive modulation. Hence, both an N CS and N EB increase can reduce V on .  Figure 8a shows the turn-off process of the SJ-RC-IGBT, SJ-IGBT, and CRC-IGBT. In the SJ-RC-IGBT, ICE falling from 90 A/cm 2 to 10 A/cm 2 needs 46 ns by a huge reduction of 95.8% compared with the CRC-IGBT and 86.7% compared with the SJ-IGBT. The high performance of the turn-off process is generally attributed to two aspects-(i) low injection of excess carriers, as shown in Figure 8b, and (ii) extracting channels, as implied in Figure 8c. (i) In the SJ-RC-IGBT, the injection of holes is at a low level, but the conductive modulation is at high level in contrast with the SJ-IGBT and CRC-IGBT. (ii) At t1, a high density of electron-hole pairs exists at all of the CS layer, N/P-pillars, and EB layer. Although from t2 to t3, the electron and hole in the main regions of the CS layer, N/Ppillars, and EB layer are remarkably reduced, a relatively high hole density remains along the left side of the gate in the CS layer and electron channel along the trench collector in the EB layer.  Figure 8a shows the turn-off process of the SJ-RC-IGBT, SJ-IGBT, and CRC-IGBT. In the SJ-RC-IGBT, I CE falling from 90 A/cm 2 to 10 A/cm 2 needs 46 ns by a huge reduction of 95.8% compared with the CRC-IGBT and 86.7% compared with the SJ-IGBT. The high performance of the turn-off process is generally attributed to two aspects-(i) low injection of excess carriers, as shown in Figure 8b, and (ii) extracting channels, as implied in Figure 8c. (i) In the SJ-RC-IGBT, the injection of holes is at a low level, but the conductive modulation is at high level in contrast with the SJ-IGBT and CRC-IGBT. (ii) At t 1 , a high density of electron-hole pairs exists at all of the CS layer, N/P-pillars, and EB layer. Although from t 2 to t 3 , the electron and hole in the main regions of the CS layer, N/P-pillars, and EB layer are remarkably reduced, a relatively high hole density remains along the left side of the gate in the CS layer and electron channel along the trench collector in the EB layer.  Figure 8a shows the turn-off process of the SJ-RC-IGBT, SJ-IGBT, and CRC-IGBT. In the SJ-RC-IGBT, ICE falling from 90 A/cm 2 to 10 A/cm 2 needs 46 ns by a huge reduction of 95.8% compared with the CRC-IGBT and 86.7% compared with the SJ-IGBT. The high performance of the turn-off process is generally attributed to two aspects-(i) low injection of excess carriers, as shown in Figure 8b, and (ii) extracting channels, as implied in Figure 8c. (i) In the SJ-RC-IGBT, the injection of holes is at a low level, but the conductive modulation is at high level in contrast with the SJ-IGBT and CRC-IGBT. (ii) At t1, a high density of electron-hole pairs exists at all of the CS layer, N/P-pillars, and EB layer. Although from t2 to t3, the electron and hole in the main regions of the CS layer, N/Ppillars, and EB layer are remarkably reduced, a relatively high hole density remains along the left side of the gate in the CS layer and electron channel along the trench collector in the EB layer.     Figure 9 shows the trade-off between Eoff and Von at ICE = 100 A/cm 2 . With an i of NEB from 1.0 × 10 16 cm −3 to 2.0 × 10 16 cm −3 , Von of the SJ-RC-IGBT is reduced from to 1.27 V at Eoff = 4.25 mJ/cm 2 , as shown in Figure 9. It can be seen that the SJ-R with EB layer (NEB = 1.0 × 10 16 cm −3 ) has Von of 1.38 V at Eoff = 4.25 mJ/cm 2 , which lower than the SJ-IGBT, as shown in Figure 9. It is worth emphasizing that the EB the SJ-RC-IGBT can enhance the conductivity in the N/P-pillars for gaining a lo due to restricting electrons leaking via the P-pillar into the N+ collector region, as th of the CS layer for blocking holes. Nevertheless, if the SJ-RC-IGBT is without the E a high speed of turn-off switching is easy to obtain in the SJ-RC-IGBT from green shown in Figure 9, but it inevitably results in improving Von. In brief, the SJ-RC-IG EB layer exhibits superior Eoff-Von trade-off over the FP-RC-IGBT [8], SJ-CSTBT [2 RC-IGBT [11], SJ-IGBT, and CRC-IGBT.  Figure 9 shows the trade-off between E off and V on at I CE = 100 A/cm 2 . With an increase of N EB from 1.0 × 10 16 cm −3 to 2.0 × 10 16 cm −3 , V on of the SJ-RC-IGBT is reduced from 1.38 V to 1.27 V at E off = 4.25 mJ/cm 2 , as shown in Figure 9. It can be seen that the SJ-RC-IGBT with EB layer (N EB = 1.0 × 10 16 cm −3 ) has V on of 1.38 V at E off = 4.25 mJ/cm 2 , which is 17% lower than the SJ-IGBT, as shown in Figure 9. It is worth emphasizing that the EB layer in the SJ-RC-IGBT can enhance the conductivity in the N/P-pillars for gaining a lower V on due to restricting electrons leaking via the P-pillar into the N+ collector region, as the effect of the CS layer for blocking holes. Nevertheless, if the SJ-RC-IGBT is without the EB layer, a high speed of turn-off switching is easy to obtain in the SJ-RC-IGBT from green dots, as shown in Figure 9, but it inevitably results in improving V on . In brief, the SJ-RC-IGBT with EB layer exhibits superior E off -V on trade-off over the FP-RC-IGBT [8], SJ-CSTBT [22], SH-RC-IGBT [11], SJ-IGBT, and CRC-IGBT. V on (V) @I CE =100 A/cm 2 Figure 9. Eoff-Von relationship of SJ-RC-IGBT, SJ-IGBT, and CRC-IGBT. Eoff-Von relationsh 100 A/cm 2 . FP-RC-IGBT is referenced from [8]. SH-RC-IGBT is referenced from [11]. SJreferenced from [22]. Figure 10 shows the key fabrication process of the SJ-RC-IGBT. First, a deep formed by reactive ion etching, and the deep trench can achieve a fairly large asp as shown in Figure 10a. Figure 10b shows the trench refilling by anisotropic growth; after epitaxy, the flat surface is achieved by chemical mechanical polish surface defects were then repaired by sacrificing oxidation. The final surface is s Figure 10b. Before forming the MOS part, the CS layer and P-body are formed by growth, as shown in Figure 10c. The rest of the facade is formed by standard tre process, with the final configuration of the emitter region and trench gate shown i 10d. The backside process is essential in the design of the RC-IGBT. First, through thinning to achieve the required width of the drift region, as shown in Figure 1 the FS layer, P+ collector, EB layer, and N+ collector are formed by backside impla as shown in Figure 10f and Figure 10g. Last, the trench collector and electrode pr the back is similar to that on the front. Through the above process flow, the SJ-R finally forms the structure shown in Figure 10h.  [8]. SH-RC-IGBT is referenced from [11]. SJ-CSTBT is referenced from [22]. Figure 10 shows the key fabrication process of the SJ-RC-IGBT. First, a deep trench is formed by reactive ion etching, and the deep trench can achieve a fairly large aspect ratio, as shown in Figure 10a. Figure 10b shows the trench refilling by anisotropic epitaxial growth; after epitaxy, the flat surface is achieved by chemical mechanical polishing. The surface defects were then repaired by sacrificing oxidation. The final surface is shown in Figure 10b. Before forming the MOS part, the CS layer and P-body are formed by epitaxial growth, as shown in Figure 10c. The rest of the facade is formed by standard trench gate process, with the final configuration of the emitter region and trench gate shown in Figure 10d. The backside process is essential in the design of the RC-IGBT. First, through the back thinning to achieve the required width of the drift region, as shown in Figure 10e, then the FS layer, P+ collector, EB layer, and N+ collector are formed by backside implantation, as shown in Figure 10f,g. Last, the trench collector and electrode process on the back is similar to that on the front. Through the above process flow, the SJ-RC-IGBT finally forms the structure shown in Figure 10h

Conclusions
A SJ-RC-IGBT with EB layer is proposed and investigated for revealing its complex conduction mechanism at the forward and reverse conditions. This innovative mechanism aids optimizing the trade-off between Eoff and Von. In comparison with the CRC-IGBT, the SJ-IGBT and SJ-RC-IGBT without EB layer and Eoff and Von in SJ-RC-IGBT with EB layer demonstrate superior advantages. Moreover, the N/P-pillars to deliver a uniform distribution of space charges without compromising the SOA at high forward conduction has considerably increased the SOA of the SJ-RC-IGBT.

Conclusions
A SJ-RC-IGBT with EB layer is proposed and investigated for revealing its complex conduction mechanism at the forward and reverse conditions. This innovative mechanism aids optimizing the trade-off between E off and V on . In comparison with the CRC-IGBT, the SJ-IGBT and SJ-RC-IGBT without EB layer and E off and V on in SJ-RC-IGBT with EB layer demonstrate superior advantages. Moreover, the N/P-pillars to deliver a uniform distribution of space charges without compromising the SOA at high forward conduction has considerably increased the SOA of the SJ-RC-IGBT.

Conflicts of Interest:
The authors declare no conflict of interest.