Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D10/00—Bipolar junction transistors [BJT]
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D18/00—Thyristors
  • H10D18/80—Bidirectional devices, e.g. triacs 
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D12/00—Bipolar devices controlled by the field effect, e.g. insulated-gate bipolar transistors [IGBT]
  • H10D12/411—Insulated-gate bipolar transistors [IGBT]
  • H10D12/441—Vertical IGBTs
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
  • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
  • H03K17/60—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being bipolar transistors
  • H03K17/66—Switching arrangements for passing the current in either direction at will; Switching arrangements for reversing the current at will
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D10/00—Bipolar junction transistors [BJT]
  • H10D10/40—Vertical BJTs
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D10/00—Bipolar junction transistors [BJT]
  • H10D10/40—Vertical BJTs
  • H10D10/441—Vertical BJTs having an emitter-base junction ending at a main surface of the body and a base-collector junction ending at a lateral surface of the body
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D12/00—Bipolar devices controlled by the field effect, e.g. insulated-gate bipolar transistors [IGBT]
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/10—Shapes, relative sizes or dispositions of the regions of the semiconductor bodies; Shapes of the semiconductor bodies
  • H10D62/102—Constructional design considerations for preventing surface leakage or controlling electric field concentration
  • H10D62/103—Constructional design considerations for preventing surface leakage or controlling electric field concentration for increasing or controlling the breakdown voltage of reverse-biased devices
  • H10D62/105—Constructional design considerations for preventing surface leakage or controlling electric field concentration for increasing or controlling the breakdown voltage of reverse-biased devices by having particular doping profiles, shapes or arrangements of PN junctions; by having supplementary regions, e.g. junction termination extension [JTE] 
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/10—Shapes, relative sizes or dispositions of the regions of the semiconductor bodies; Shapes of the semiconductor bodies
  • H10D62/102—Constructional design considerations for preventing surface leakage or controlling electric field concentration
  • H10D62/103—Constructional design considerations for preventing surface leakage or controlling electric field concentration for increasing or controlling the breakdown voltage of reverse-biased devices
  • H10D62/105—Constructional design considerations for preventing surface leakage or controlling electric field concentration for increasing or controlling the breakdown voltage of reverse-biased devices by having particular doping profiles, shapes or arrangements of PN junctions; by having supplementary regions, e.g. junction termination extension [JTE] 
  • H10D62/106—Constructional design considerations for preventing surface leakage or controlling electric field concentration for increasing or controlling the breakdown voltage of reverse-biased devices by having particular doping profiles, shapes or arrangements of PN junctions; by having supplementary regions, e.g. junction termination extension [JTE]  having supplementary regions doped oppositely to or in rectifying contact with regions of the semiconductor bodies, e.g. guard rings with PN or Schottky junctions
  • H10D62/107—Buried supplementary regions, e.g. buried guard rings 
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/10—Shapes, relative sizes or dispositions of the regions of the semiconductor bodies; Shapes of the semiconductor bodies
  • H10D62/113—Isolations within a component, i.e. internal isolations
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/10—Shapes, relative sizes or dispositions of the regions of the semiconductor bodies; Shapes of the semiconductor bodies
  • H10D62/113—Isolations within a component, i.e. internal isolations
  • H10D62/115—Dielectric isolations, e.g. air gaps
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/10—Shapes, relative sizes or dispositions of the regions of the semiconductor bodies; Shapes of the semiconductor bodies
  • H10D62/13—Semiconductor regions connected to electrodes carrying current to be rectified, amplified or switched, e.g. source or drain regions
  • H10D62/133—Emitter regions of BJTs
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/10—Shapes, relative sizes or dispositions of the regions of the semiconductor bodies; Shapes of the semiconductor bodies
  • H10D62/13—Semiconductor regions connected to electrodes carrying current to be rectified, amplified or switched, e.g. source or drain regions
  • H10D62/137—Collector regions of BJTs
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/10—Shapes, relative sizes or dispositions of the regions of the semiconductor bodies; Shapes of the semiconductor bodies
  • H10D62/17—Semiconductor regions connected to electrodes not carrying current to be rectified, amplified or switched, e.g. channel regions
  • H10D62/177—Base regions of bipolar transistors, e.g. BJTs or IGBTs
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D64/00—Electrodes of devices having potential barriers
  • H10D64/111—Field plates
  • H10D64/112—Field plates comprising multiple field plate segments
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D64/00—Electrodes of devices having potential barriers
  • H10D64/111—Field plates
  • H10D64/117—Recessed field plates, e.g. trench field plates or buried field plates
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D64/00—Electrodes of devices having potential barriers
  • H10D64/20—Electrodes characterised by their shapes, relative sizes or dispositions 
  • H10D64/27—Electrodes not carrying the current to be rectified, amplified, oscillated or switched, e.g. gates
  • H10D64/281—Base electrodes for bipolar transistors
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W42/00—Arrangements for protection of devices
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D48/00—Individual devices not covered by groups H10D1/00 - H10D44/00
  • H10D48/30—Devices controlled by electric currents or voltages
  • H10D48/32—Devices controlled by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
  • H10D48/34—Bipolar devices
  • H10D48/341—Unijunction transistors, i.e. double base diodes

Definitions

• the present application relates to Double-Base Bidirectional
• Bipolar transistors and more particularly to power transistors of the general type known as "B-TRANs.”
• the emitter/collector regions are laterally separated from the base contact regions by a dielectric-filled trench. This reduces same-side carrier recombination in the ON state.
• Application US 2014-0375287 also describes some surprising aspects of operation of the device. Notably: 1) when the device is turned on, it is preferably first operated merely as a diode, and base drive is then applied to reduce the on- state voltage drop. 2) Base drive is preferably applied to the base nearest whichever emitter/collector region will be acting as the collector (as determined by the external voltage seen at the device terminals). 3) A two-stage turnoff sequence is preferably used. 4) In the off state, base-emitter voltage (on each side) is limited by a low- voltage diode which parallels that base-emitter junction.
• the present application teaches, among other innovations, a symmetrically bidirectional dual-contact base bipolar junction transistor, in which both of the emitter/collector regions, which are present on both (opposed) surfaces of a semiconductor die, are surrounded by a field plate in a trench.
• This field plate separates the emitter/collector regions from adjacent base contact regions. Since base contact regions are present on both surfaces of the device, this structure improves the breakdown voltage of whichever base contact region is on the collector side, without degrading the characteristics of the base contact region on the other side. This provides surprising improvement in the breakdown voltage of a device like that of US 2014-0375287.
• the present application also teaches, among other innovations, methods of operating structures of this type, and systems which incorporate structures of this type.
• Figure 1 schematically shows an exemplary B-TRAN having trenched field plates.
• Figure 2 shows the preferred circuit symbol for a B-TRAN- type device.
• FIG. 3 schematically shows one sample embodiment of a B- TRAN having dielectric-filled trenches, as described in published application US 2014-0375287, which is hereby incorporated by reference.
• Figure 4A shows an exemplary doping profile in a device like that of Figure 1.
• Figure 4B shows the distribution of potential, in a device like that of Figure 1 , at breakdown.
• Figure 5A shows the electric field, in a device like that of
• Figure 1 at breakdown.
• Figure 5B shows impact ionization, in a device like that of Figure 1, at breakdown.
• Figure 6 shows the distribution of current density magnitude, in a device like that of Figure 1, at breakdown.
• Figure 7 shows a current density distribution plot, with current vectors indicated, for the upper side of a device like that of Figure 1 , at breakdown.
• Figure 8 shows a current density distribution plot, with current vectors indicated, like that of Figure 6, at breakdown, for the lower side of a device like that of Figure 1.
• Figure 9 shows a plan view of one surface of a device like that of Figure 1, showing how the emitter/collector areas are laterally surrounded by vertical field plates.
• Figure 10 is a partial cross-section of the periphery of a device like that of Figure ⁇ , showing doping profiles generally.
• B-TRAN The class of fully bidirectional bipolar double-base transistors described in Published U.S. application US 2014-0375287 is now commonly referred to as a "B-TRAN.”
• the emitter/collector regions are laterally separated from the base contact regions by a dielectric-filled trench.
• a B-TRAN is a three- layer four-terminal bidirectional bipolar transistor, as shown in the sample embodiment of Figure 1. It is a symmetrical device, meaning that the polarity of the voltage on the two "end" terminals 102 and 104 determines which of these two terminals functions as the emitter (i.e., has a forward biased junction), and which of these terminals functions as the collector (i.e., has a reverse biased junction).
• V C E-SAT minimum on-voltage
• a B-TRAN is in the "active off-state" when the e-base (base on emitter side) is shorted to the emitter, and the c-base (base on the
• collector side is open.
• the collector is the anode (high voltage side)
• the emitter is the cathode (low voltage side).
• the B-TRAN is also off when both bases are open, but due to the relatively high gain of the B-TRAN in this state, the breakdown voltage is low.
• the series combination of a normally-ON switch and a diode attached between each base and its respective emitter/collector, as disclosed elsewhere, will significantly increase the blocking voltage in this "passive off-state". The switches are turned off during normal operation.
• Figure 3 shows a fully symmetric bidirectional bipolar transistor, in which emitter/collector and base contact regions are separated by dielectric-filled trenches.
• This structure is described in published application US 2014-0375287.
• the example shown is an npn device, in which n-type emitter/collector regions are present on both front and back faces of a p-type semiconductor die.
• separate p-type base contact regions are provided on both front and back surfaces, to provide connection to the bulk of the p-type semiconductor material.
• the whole thickness of the semiconductor die can be regarded as the base, but the two base contact regions are electrically distinct, and are operated separately.
• This reduction in device performance may be reduced or eliminated by the combination of dielectric layer 108 adjacent to the sidewall and bottom of trench 106, and field plate 110 in the center of the trench connected to the n-type junction, as shown in Figure 1.
• the thickness of dielectric 108 must be chosen so the intensity of the electric field below the bottom of trench 106 is reduced to an acceptable level for the device being manufactured. However, simulations have shown that for a layer of silicon dioxide, a thickness in the range of 0.2 ⁇ is sufficient for a device having a 1200 Volt breakdown.
• FIG 8 embodiment has a breakdown voltage of 1223 V, and an open c-base voltage of 1195.23 V.
• Figure 4B shows an exemplary plot of potential at breakdown for a device like that simulated in Figure 4A.
• the sample embodiment of Figure 6 plots the distribution of current density, near the emitter/collector region acting as a collector, at breakdown for a device like that of Figure 1.
• this current density distribution is supplemented by vectors showing the direction of current near the collector of a device like that of Figure 1.
• the sample embodiment of Figure 8 shows current density distribution and current direction near the emitter of a device like that of Figure 1.
• Figure 9 shows a plan view of one surface of a device like that of Figure 1, showing how the emitter/collector areas are laterally surrounded by vertical field plates.
• Figure 10 is a partial cross-section of the periphery of a device like that of Figure 1 , showing doping profiles generally. Note that only two field-limiting rings are shown in this example, but in practice the number of field-limiting rings can be much larger, e.g. ten.
• the active region contains the emitter regions, each of which is surrounded by a vertical field plate. There are base contact regions adjacent to the long edge of each emitter region.
• a field plate that surrounds the entire active region. It extends outward over the P- region at the edge of the active region, and into the region that has a thick field oxide region.
• FL s field limiting rings
• the dopings shown as n- are preferably the same Phosphorus dopings as those used in the emitter/collector regions.
• the emitter/collector regions themselves also have a shallower n+ contact doping, which is not present in the n- periphery regions. This is preferably As (arsenic).
• the dopings shown as p- are preferably the same boron dopings as those used in the emitter/collector regions.
• the p- doping is the bulk doping of the semiconductor die.
• This can be, for example, 180-250 ohm-cm for a 1200V part, 80- 120 ohm-cm for a 600V part, and higher for higher rated voltages.
• Dual-base two-sided bipolar power transistors which use an insulated field plate to separate the emitter/collector diffusions from the nearest base contact diffusion. This provides a surprising improvement in turn-off performance, and in breakdown voltage.
• a power semiconductor device comprising: first and second first-conductivity-type emitter/collector regions, located respectively on first and second surfaces of a second-conductivity-type semiconductor die having first and second surfaces; first and second second- conductivity-type base contact regions, located respectively on the first and second surface of the semiconductor die; first and second insulated field plate structures, located respectively on the first and second surface of the semiconductor die; wherein the field plate structures are conductive, and are vertically extended, and laterally adjoin the emitter/collector regions; wherein the first emitter/collector region is generally shaped like a stripe with sides and ends, and is laterally surrounded by the first insulated field plate structure at both sides and both ends, and is electrically connected to the first insulated field plate
• the second emitter/collector region is generally shaped like a stripe with sides and ends, and is laterally surrounded by the second insulated field plate structure at both sides and both ends, and is electrically connected to the second insulated field plate structure; whereby the breakdown voltage is improved under either polarity of applied voltage.
• a power semiconductor device comprising: a p-type semiconductor die having first and second surfaces; first and second n- type emitter/collector regions, located respectively on the first and second surface of the semiconductor die; first and second p-type base contact regions, located respectively on the first and second surface of the semiconductor die; first and second trenched field plate structures, located respectively on the first and second surface of the semiconductor die; wherein the first emitter/collector region is electrically connected to, and is entirely surrounded by, the first trenched field plate structure; and wherein the second emitter/collector region is electrically connected to, and is entirely surrounded by, the second trenched field plate structure; whereby the breakdown voltage is improved under either polarity of applied voltage.
• a power semiconductor device comprising: an n-type semiconductor die having first and second surfaces; first and second p- type emitter/collector regions, located respectively on the first and second surface of the semiconductor die; first and second n-type base contact regions, located respectively on the first and second surface of the semiconductor die; first and second trenched field plate structures,
• first emitter/collector region located respectively on the first and second surface of the semiconductor die; wherein the first emitter/collector region is electrically connected to, and is entirely surrounded by, the first trenched field plate structure; and wherein the second emitter/collector region is electrically connected to, and is entirely surrounded by, the second trenched field plate structure; whereby the breakdown voltage is improved under either polarity of applied voltage.
• a method for switching comprising: in the ON state, driving base current through one, but not both, of first and second p-type base contact regions which are located on opposite faces of a p-type substrate, to thereby allow passage of current between first and second n-type emitter/collector regions which are also located on opposite faces of the p-type substrate; wherein the base contact regions and the emitter/collector regions are laterally separated, on both faces of the substrate, by a vertically extended conductive field plate which is laterally surrounded by dielectric material; and in the OFF state, reducing peak electric field near the emitter-base junctions by capacitive coupling to the insulated field plate.
• a method for switching comprising: in the ON state, driving base current through one, but not both, of first and second n-type base contact regions which are located on opposite faces of a n-type substrate, to thereby allow passage of current between first and second p-type emitter/collector regions which are also located on opposite faces of the n-type substrate; wherein the base contact regions and the emitter/collector regions are laterally separated, on both faces of the
• a method for switching a power bipolar semiconductor device which includes both an n-type emitter/collector region, and also a p-type base contact region, on both first and second surfaces of a p-type semiconductor die, comprising: during the ON state, driving base current into one of the base contact regions; and during transition to the OFF state, temporarily shorting the base contact region on the first surface to the emitter/collector region on the first surface, while also shorting the base contact region on the second surface to the emitter/collector region on the second surface, and thereafter floating at least the base contact region on the first surface; wherein the base contact region on the first surface is not connected to the base contact region on the second surface; wherein a trenched field plate separates each emitter/collector region from the respective base contact region; whereby currents of both polarities are controllably switched between the emitter/collector regions on opposite surfaces.
• a switching circuit comprising: a two-base bidirectional npn semiconductor device which includes both n-type emitter/collector regions, and also p-type base contact regions, on both opposed surfaces of a p-type monolithic semiconductor die; control circuitry which is connected separately to the first and second base contact regions on the opposed surfaces; first and second distinct clamp circuits, each
• a method for switching a power semiconductor device which includes both an n-type emitter/collector region, and also a p-type base contact region, on both first and second surfaces of a p-type semiconductor die, comprising: in the ON state, flowing base current through the base contact region which is nearer the more positive one of the emitter/collector regions, without flowing base current through the other of the base contact regions; wherein the base contact region on the first surface is not electrically connected to the base contact region on the second surface, except through the semiconductor die itself; wherein the emitter/collector region on the first surface is not electrically connected to the emitter/collector region on the second surface; and wherein a trenched field plate separates each emitter/collector region from the respective base contact region; whereby bidirectional switching is achieved with low on-state voltage drop and reliable turn-off.
• a method for switching a power semiconductor device which includes both an n-type emitter/collector region, and also a p-type base contact region, on both first and second surfaces of a p-type semiconductor die, comprising: at turn-on, shorting the more positive one of the emitter/collector regions together with the base contact region on the same one of the surfaces, to thereby conduct current with a diode voltage drop; and thereafter flowing base current through at least one of the base contact regions, to initiate conduction as a bipolar transistor with less than a diode voltage drop; wherein the base contact region on the first surface is not electrically connected to the base contact region on the second surface, except through the semiconductor die itself; wherein a trenched field plate separates each emitter/collector region from the corresponding base contact region; whereby bidirectional switching is achieved with low on-state voltage drop and reliable turn-off.
• the semiconductor die is silicon, but other semiconductor materials can be used instead.
• the field plate is preferably made of doped polysilicon, but other conductive materials, such as aluminum or tungsten, can also be used.
• the insulation around the field plate is preferably thick enough to withstand the large voltage drop seen at the collector side in the off state. Moreover, the insulation around the field plate can be more robust, if desired.
• the insulation around the field plate is provided by a thin layer of silicon dioxide which is grown on the sidewalls of a trench etched into the (silicon) die.
• this layer of insulation can alternatively include multiple different materials.

Landscapes

• Bipolar Transistors (AREA)
• Electrodes Of Semiconductors (AREA)
• Bipolar Integrated Circuits (AREA)

Priority Applications (8)

Applications Claiming Priority (2)

Related Child Applications (1)

Publications (1)

Family

ID=55747235

Family Applications (1)

Country Status (7)

Cited By (1)

Families Citing this family (13)

Citations (5)

Family Cites Families (14)

• 2015
  • 2015-10-13 GB GB1608361.0A patent/GB2535381B/en active Active
  • 2015-10-13 KR KR1020177008934A patent/KR102382856B1/ko active Active
  • 2015-10-13 EP EP15850860.6A patent/EP3155664B1/en active Active
  • 2015-10-13 WO PCT/US2015/055388 patent/WO2016061140A1/en not_active Ceased
  • 2015-10-13 JP JP2017519858A patent/JP6559232B2/ja active Active
  • 2015-10-13 CN CN201580054265.2A patent/CN106796951B/zh active Active
• 2017
  • 2017-04-13 US US15/486,921 patent/US10418471B2/en active Active
• 2019
  • 2019-08-30 US US16/557,284 patent/US10580885B1/en active Active
• 2020
  • 2020-01-27 US US16/773,031 patent/US10892354B2/en active Active

Patent Citations (5)

Also Published As

Similar Documents

Legal Events