News Column

Patent Issued for Semiconductor Power Modules and Devices

February 26, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventor Wu, Yifeng (Goleta, CA), filed on February 24, 2012, was published online on February 11, 2014.

The assignee for this patent, patent number 8648643, is Transphorm Inc. (Goleta, CA).

Reporters obtained the following quote from the background information supplied by the inventors: "Power switching circuits such as bridge circuits are commonly used in a variety of applications. A circuit schematic of a 3-phase bridge circuit 10 configured to drive a motor is shown in FIG. 1. Each of the three half bridges 15, 25, and 35 in circuit 10 includes two transistors, 41 and 42, 43 and 44, and 45 and 46, respectively, which are able to block voltage in a first direction and are capable of conducting current in the first direction or optionally in both directions. In applications where the transistors employed in the bridge circuit 10 are only capable of conducting current in one direction, for example when silicon IGBTs are used, an anti-parallel diode (not shown) may be connected to each of the transistors 41-46. Each of transistors 41-46 is capable of blocking a voltage at least as large as the high voltage (HV) source 11 of the circuit 10 when they are biased in the OFF state. That is, when the gate-source voltage V.sub.GS of any of transistors 41-46 is less than the transistor threshold voltage V.sub.th, no substantial current flows through the transistor when the drain-source voltage V.sub.DS (i.e., the voltage at the drain relative to the source) is between 0V and HV. When biased in the ON state (i.e., with V.sub.GS greater than the transistor threshold voltage), the transistors 41-46 are each capable of conducting sufficiently high current for the application in which they are used.

"The transistors 41-46 may be enhancement mode or E-mode transistors (normally off, V.sub.th>0), or depletion mode or D-mode (normally on, V.sub.th

"FIG. 2a shows half bridge 15 of the full 3-phase motor drive in FIG. 1, along with the winding of the motor (represented by inductive component 21) between nodes 17 and 18. Also shown is transistor 44, into which the motor current feeds. For this phase of power, transistor 44 is continuously ON (V.sub.gs44>V.sub.th) and transistor 42 is continuously OFF (V.sub.gs42

"As used herein, the term 'blocking a voltage' refers to a transistor, device, or component being in a state for which significant current, such as current that is greater than 0.001 times the average operating current during regular ON-state conduction, is prevented from flowing through the transistor, device, or component when a voltage is applied across the transistor, device, or component. In other words, while a transistor, device, or component is blocking a voltage that is applied across it, the total current passing through the transistor, device, or component will not be greater than 0.001 times the average operating current during regular ON-state conduction.

"Referring to FIG. 2c, when transistor 41 is switched OFF, no current can flow through transistor 41, so the motor current flows in the reverse direction through transistor 42, which can occur whether transistor 42 is biased ON or OFF. Alternatively, an anti-parallel freewheeling diode (not shown) can be connected across transistor 42, in which case the reverse current flows through the freewheeling diode. During such operation, the inductive component 21 forces the voltage at node 17 to a sufficiently negative value to cause reverse conduction through transistor 42, and transistor 41 blocks a voltage which is close to HV.

"FIGS. 3a-3c show operation of the half bridge 15 under conditions where current passes through the inductive load in the opposite direction as compared to that shown in FIGS. 2a-2c, and the voltage at node 17 is controlled by switching the low-side transistor 42. For the mode of operation illustrated in FIGS. 3a-3c, the motor current 27 is fed into the inductive motor 21 through transistor 43. During this mode of operation, transistor 43 is continuously ON (V.sub.gs43>V.sub.th) and transistor 41 is continuously OFF (V.sub.gs41

"Referring to FIG. 3c, when transistor 42 is switched OFF, no current can flow through transistor 42, so the motor current flows in the reverse direction through transistor 41, which can occur whether transistor 41 is biased ON or OFF. Alternatively, an anti-parallel freewheeling diode (not shown) can be connected across transistor 41, in which case the reverse current flows through the freewheeling diode. During such operation, the inductive component 21 forces the voltage at node 17 to a sufficiently high value (slightly higher than HV) to cause reverse conduction through transistor 41, and transistor 42 blocks a voltage which is close to or slightly higher than HV.

"In addition to their use in motor-drive applications, half bridges and bridge circuits can also be used in many other applications, for example boost or buck converters or in power supplies. An exemplary circuit which utilizes a half bridge 15 to drive an electrical load 28 is illustrated in FIG. 4. The electrical load 28 can, for example, be capacitive and/or resistive, or in some cases could be a battery or DC power supply. As further illustrated in FIG. 4, in many applications a filter 22, which can include inductive and/or capacitive elements 23 and 24, respectively, is inserted between the half bridge 15 and the electrical load 28.

"The mode of switching illustrated in FIGS. 2a-2c and 3a-3c is commonly known as hard-switching. A hard-switching circuit configuration is one in which the switching transistors are configured to have high currents passing through them as soon as they are switched ON, and to have high voltages across them as soon as they are switched OFF. In other words, the transistors are switched ON during periods where non-zero currents flow through the inductive load, so substantial current flows through the transistors immediately or soon after the transistors are switched ON, rather than the current rising gradually. Similarly, the transistors are switched OFF during periods where high voltages must be blocked by the transistors, so substantial voltage is blocked by the transistors immediately or soon after the transistors are switched OFF, rather than the voltage rising gradually. Transistors switched under these conditions are said to be 'hard-switched'.

"Alternative circuit configurations make use of additional passive and/or active components, or alternatively signal timing techniques, to allow the transistors to be 'soft-switched'. A soft-switching circuit configuration is one in which the switching transistors are configured to be switched ON during zero-current (or near zero-current) conditions and switched OFF during zero-voltage (or near zero-voltage) conditions. Soft-switching methods and configurations have been developed to address the high levels of electro-magnetic interference (EMI) and associated ringing observed in hard-switched circuits, especially in high current and/or high voltage applications. While soft-switching can in many cases alleviate these problems, the circuitry required for soft switching typically includes many additional components, resulting in increased overall cost and complexity. Soft-switching also typically requires that the circuits be configured to switch only at specific times when the zero-current or zero-voltage conditions are met, hence limiting the control signals that can be applied and in many cases reducing circuit performance. Hence, alternative configurations and methods are desirable for hard-switched power switching circuits in order to maintain sufficiently low levels of EMI."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventor's summary information for this patent: "In one aspect, an electronic component is described which includes a first transistor encased in a first package, the first package including a first conductive portion having a first area, with the first transistor being mounted over the first conductive portion. The electronic component further includes a second transistor encased in a second package, the second package including a second conductive portion having a second area, the second transistor being mounted over the second conductive portion. The electronic component also includes a substrate comprising an insulating layer between a first metal layer and a second metal layer, the first metal layer being on a first side of the substrate and the second metal layer being on a second side of the substrate. The first package is on the first side of the substrate with the first conductive portion being electrically connected to the first metal layer, the second package is on the second side of the substrate with the second conductive portion being electrically connected to the second metal layer, and the first package is opposite the second package, with at least 50% of the first area of the first conductive portion being opposite the second area of the second conductive portion.

"In another aspect, an electronic component is described which includes a first transistor encased in a first package, the first package having a source lead and a first conductive portion, with the first transistor being mounted over the first conductive portion. The electronic component also includes a second transistor encased in a second package, the second package having a drain lead and a second conductive portion, with the second transistor being mounted over the second conductive portion. The electronic component further includes a substrate comprising an insulating layer between a first metal layer and a second metal layer, the first metal layer being on a first side of the substrate and the second metal layer being on a second side of the substrate. The first package is on the first side of the substrate with the first conductive portion being electrically connected to the first metal layer, the second package is on the second side of the substrate with the second conductive portion being electrically connected to the second metal layer, and the first package is at least partially opposite the second package, with the source lead of the first package being substantially aligned with the drain lead of the second package.

"In yet another aspect, an electronic component is described which includes a capacitor comprising an insulating layer between a first electrically conductive layer and a second electrically conductive layer. The electronic component also includes a first transistor encased in a first package, the first package having a first conductive portion, and a second transistor encased in a second package, the second package having a second conductive portion. The first conductive portion is mounted directly over the first electrically conductive layer, and the second conductive portion is mounted directly over the second electrically conductive layer.

"In still another aspect, a half bridge configured to be connected to an electrical load is described. The half bridge includes a first switch encased in a first package and a second switch encased in a second package, the first package having a source lead and the second package having a drain lead, with the source lead of the first package being electrically connected to the drain lead of the second package. The half bridge is operable to hard-switch a voltage of at least 300 Volts across the electrical load at a switching rate of at least 100 Volts/nanosecond while a current of at least 3 Amps flows through the electrical load.

"The electronic components and half bridges described herein can include one or more of the following features. The first and second transistors can be part of a half bridge circuit. The substrate can form a capacitor which serves to stabilize a voltage between the first and second metal layers during operation of the half bridge circuit. The capacitor formed by the substrate can be a first capacitor, the electronic component further comprising a second capacitor connected in parallel to the first capacitor. The substrate can include a via hole, and a lead of the second capacitor can pass through the via hole. The first package can have a source lead and the second package can have a drain lead, with the source and drain leads being electrically connected to one another. The substrate can include a via hole, and a connector which electrically connects the source lead of the first package to the drain lead of the second package can pass through the via hole. The first transistor can have a first electrode which is electrically connected to the first conductive portion, and the second transistor can have a second electrode which is electrically connected to the second conductive portion. The first electrode can be a drain electrode of the first transistor, and the second electrode can be a source electrode of the second transistor. The first conductive portion can be directly on and contacting the first metal layer, and the second conductive portion can be directly on and contacting the second metal layer.

"The first transistor or the second transistor can be a III-Nitride transistor or a lateral device. The first package can have a source lead and the second package can have a drain lead, with the source lead being substantially aligned with the drain lead. The electronic component can further include a third transistor encased in the first package, where a source of the first transistor is electrically connected to a drain of the third transistor, and a gate of the first transistor is electrically connected to a source of the second transistor. The first transistor can be a high-voltage depletion-mode transistor, and the third transistor can be a low-voltage enhancement-mode transistor.

"The substrate can be a printed circuit board (PCB) substrate, such as a 2-layer printed circuit board (PCB) substrate. A drain electrode of the first transistor can be electrically connected to the first conductive portion, and a source electrode of the second transistor can be electrically connected to the second conductive portion. The first package can have a drain lead and the second package can have a source lead, with the drain lead of the first package electrically connected to the first conductive portion, and the source lead of the second package electrically connected to the second conductive portion. The electronic component can comprise a half bridge module, which can be configured to be connected to an electrical load. The first conductive portion can be electrically connected to the first electrically conductive layer, and the second conductive portion can be electrically connected to the second electrically conductive layer. The current through an electrical load can be at least 6 amps, and the first switch and the second switch can be on opposite sides of a substrate.

"In yet another aspect, a method of operating a half bridge circuit comprising a first switch encased in a first package and a second switch encased in a second package is described. The method includes biasing a drain of the first switch at a voltage of at least 300 Volts relative to a source of the second switch, and biasing the first switch on and biasing the second switch off, thereby causing a current of at least 3 Amps to flow through the first switch and causing the second switch to block a voltage. The method further includes at a first time switching the first switch off, causing the current to flow through the second switch and causing the first switch to block a voltage. The switching of the first switch comprises hard-switching of the first switch at a switching rate of at least 100 Volts/nanosecond.

"Methods described herein can each include one or more of the following features. The first switch and the second switch can each comprise one or more transistors. The method can further comprise at a second time switching the first switch from off to on, causing the current to flow through the first switch and causing the second switch to block a voltage. The second time can be after the first time. The method can further comprise connecting the half bridge circuit to an electrical load, wherein the current flows through the electrical load. The drain of the first switch can be biased at a voltage of at least 400 Volts relative to the source of the second switch.

"The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims."

For more information, see this patent: Wu, Yifeng. Semiconductor Power Modules and Devices. U.S. Patent Number 8648643, filed February 24, 2012, and published online on February 11, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=49&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=2448&f=G&l=50&co1=AND&d=PTXT&s1=20140211.PD.&OS=ISD/20140211&RS=ISD/20140211

Keywords for this news article include: Electronics, High Voltage, Circuit Board, Semiconductor, Transphorm Inc.

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Source: Electronics Newsweekly


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