Abstract:
Methods and structures provide galvanic isolation for electrical systems using a wide oxide filled trench, and that allows power across the system divide with a transformer, and that transmits data at a high baud rate using an optical link. The system solution allows the integration of all of these elements onto a single semiconductor substrate in contrast to currently available galvanic isolation systems that require multiple individual silicon die that are connected by wire bonds and are relatively slow.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/297,044, filed on Jan. 21, 2010. Provisional Application No. 61/297,044 is hereby incorporated by reference herein in its entirety. 
         [0002]    This application also claims the benefit of U.S. Provisional Application No. 61/297,451, filed on Feb. 8, 2010. Provisional Application No. 61/297,451 is hereby incorporated by reference herein in its entirety. 
         [0003]    This application is related to co-pending and commonly-assigned U.S. application Ser. No. 12/315,934, filed on Dec. 8, 2008, and titled “Method of Forming High Lateral Voltage Isolation Structure Involving Two Separate Trench Fills.” application Ser. No. 12/315,934 is hereby incorporated by reference herein in its entirety. 
         [0004]    This application is also related to co-pending and commonly-assigned U.S. application Ser. No. 12/584,904, filed on Sep. 15, 2009, and titled “High-Speed Avalanche Light Emitting Diode (ALED) and Related Apparatus and Method.” application Ser. No. 12/584,904 is hereby incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0005]    This disclosure relates to galvanic isolation in an electrical system and, in particular, to a galvanic isolation technique that combines optical coupling with transformer and trench technology to provide a galvanic isolation system that can be integrated onto a single semiconductor substrate. 
       BACKGROUND 
       [0006]    Any electrical system that includes systems that have different ground references or that have the capability to produce current surges is required to incorporate galvanic isolation to protect both the system and the user. 
         [0007]    There are a number of solutions available that offer galvanic isolation between two electrical systems. One such solution is a multi-die approach that includes a transformer connected between the two systems. Data are transferred across the transformer via magnetic fields by utilizing the first system to apply short pulses on one side; these pulses are transmitted across the transformer and the data are decoded on the other side by the second system. Another solution is similar to that just described, but uses a capacitor to isolate two electrical systems instead of a transformer. Yet another solution utilizes optical coupling whereby a light emitting diode (LED) in a first system emits light and a photodiode in the second system detects the light and generates electrical current; the LED and photodiode are typically built from III-V or II-VI semiconductor materials such as GaAs and InGaAs, with the LED and the photodiode being physically distinct units. 
         [0008]    Currently available galvanic isolation solutions require multiple individual semiconductor die that are connected by wire bonds and are relatively slow. There is a need for a high speed galvanic isolation system that allows for the integration of all of the system elements onto a single semiconductor substrate. 
       SUMMARY 
       [0009]    Disclosed embodiments provide galvanic isolation methods and structures for two electrical systems using a wide dielectric galvanic isolation barrier, and that allow power to be provided across the system divide utilizing a transformer, and that transmit data at a high baud rate using an optical link. The system solution allows the integration of all of these elements onto a single semiconductor substrate. 
         [0010]    Disclosed embodiments provide a system for galvanic isolation of a first electrical system that is formed in a semiconductor substrate and that includes first electrical circuitry that operates at a first voltage level and a second electrical system that is formed in the semiconductor substrate and that includes second circuitry that operates at a second voltage level that is different than the first voltage level. The system comprises: a dielectric galvanic isolation barrier formed in the semiconductor substrate between the first electrical system and the second electrical system; one or more optical emitters formed in the semiconductor substrate as part of the first electrical system and that generates light pulses that are transmitted through the dielectric galvanic isolation barrier to the second electrical system; one or more optical receivers formed in the semiconductor substrate as part of the second electrical system and adapted to receive light pulses transmitted through the dielectric galvanic isolation barrier; a clock generator formed in the semiconductor substrate as part of the first electrical system and that provides a clock signal to the one or more optical emitters to define the light pulses generated by the optical emitters; power circuitry formed in the semiconductor substrate as part of the first electrical system and that provides a power signal; and a transformer structure formed on the semiconductor substrate and adapted to transmit the clock signal and the power signal from the first electrical system to the second electrical system. 
         [0011]    Disclosed embodiments provide a method for providing galvanic isolation in a system that includes a first electrical system formed in a semiconductor substrate, the first electrical system including first electrical circuitry that operates at a first voltage level, and a second electrical system formed in the semiconductor substrate, the second electrical system including second electrical circuitry that operates at a second voltage level that is different than the first voltage level. The methods comprises: forming a dielectric galvanic isolation barrier in the semiconductor substrate between the first electrical system and the second electrical system; forming one or more optical emitters in the semiconductor substrate as part of the first electrical system, the one or more optical emitters being operable to generate light pulses that are transmitted through the dielectric galvanic isolation barrier to the second electrical system; forming one or more optical receivers in the semiconductor substrate as part of the second electrical system, the one or more optical receivers being operable to receive the light pulses transmitted through the dielectric galvanic isolation barrier; forming a clock generator in the semiconductor substrate as part of the first electrical system, the clock generator being operable to provide a clock signal to the one or more optical emitters to define the light pulses generated by the one or more optical emitters; forming power circuitry in the semiconductor substrate as part of the first electrical system, the power circuitry being operable to provide a power signal; and forming a transformer structure on the semiconductor substrate, the transformer structure being adapted to transmit the clock signal and the power signal from the first electrical system to the second electrical system. 
         [0012]    Features and advantages of the various aspects of the disclosed subject matter will be more fully understood and appreciated upon consideration of the following detailed description and the accompanying drawings, which set forth illustrative embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a block diagram illustrating an embodiment of a single-chip galvanic isolation system. 
           [0014]      FIG. 2  is a schematic diagram illustrating an embodiment of a single-chip galvanic isolation system. 
           [0015]      FIGS. 3A and 3B  illustrate an embodiment of an avalanche light emitting diode (ALED). 
           [0016]      FIG. 4  is a cross section drawing illustrating light transmission through a dielectric galvanic isolation barrier. 
           [0017]      FIG. 5  is a cross section drawing illustrating an embodiment of a galvanic isolation transformer integrated into a single semiconductor substrate. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  shows a system  100  that includes two electrical systems: a first electrical system A that includes first electrical circuitry  102  that operates at a first voltage level (e.g., 5000V) and a second electrical system B that includes second electrical circuitry  104  that operates at a second voltage level that is different than the first voltage level (e.g., 5V). Both the first electrical circuitry  102  and the second electrical circuitry  104  are formed in a single semiconductor substrate (e.g., silicon)  106  and separated by a dielectric galvanic isolation barrier  108 , e.g. silicon dioxide, that is formed in the semiconductor substrate  106 . 
         [0019]      FIG. 1  also shows a galvanic isolation system  110  that is formed in the semiconductor substrate  106 . In addition to the dielectric galvanic isolation barrier  108 , the galvanic isolation system  110  includes one or more optical emitters  112  that are formed in the semiconductor substrate  106  as part of the first electrical system A. The one or more optical emitters  112  generate light pulses  114  that are defined by the frequency of a clock signal  116  that is generated by a clock generator  118  that is also formed in the semiconductor substrate  106  as part of the first electrical system A. The light pulses  114  that are generated by the optical emitters  112 , and which may correspond to data output signals  120  from the first electrical circuitry  102 , are transmitted across the dielectric galvanic isolation barrier  108  from the first electrical system A to the second electrical system B. The clock signal  116  is also transmitted across a transformer structure  122  that is formed on the semiconductor substrate  106  to the second electrical system B. As shown in  FIG. 1 , one or more high speed optical receivers  124  formed in the semiconductor substrate  106  as part of the second electrical system B detect the transmitted light pulses which are converted into current and amplified by sense circuitry (not shown) in the conventional manner, and provided to the second electrical circuitry  104  as data input signals  126 . The clock signal  116  is used as a refresh signal to the optical receivers  124  to both control timing and increase the speed. As further shown in  FIG. 1 , power circuitry  128  formed in the semiconductor substrate  106  as part of the first electrical system A provides a power signal  130  that is transmitted by the transformer structure  122  from the first electrical system A to the second electrical system B. Thus, the galvanic isolation system  110  enables high speed data communication across the galvanic isolation barrier  108  while at the same time allowing integration of all of the elements of the galvanic isolation system onto a single semiconductor substrate. 
         [0020]      FIG. 2  provides a schematic representation of an embodiment of a galvanic isolation system  200  having multi-channel capability. As shown in  FIG. 2 , data is transmitted from a plurality of silicon LEDs  202  to a corresponding plurality of silicon photodiodes  204 . The silicon photodiodes  204  incorporate a reset feature using the high frequency clock signal  206  that is tapped off the main transformer  208 . This is the data rate. The reset feature flushes carriers from the photodiodes  204 , thereby increasing their operating data rate. As further shown in  FIG. 2 , power is transmitted across the transformer  208  using a resonant LC system at high frequency, e.g., 500 MHz to several GHz. Power is extracted across the transformer  208  and is, therefore, isolated. 
         [0021]    Element of the  FIG. 1  and  FIG. 2  embodiments will now be described in greater detail. 
         [0022]    Optical Emitters 
         [0023]    Light emitting diodes (LEDs), created in silicon, may be used to generate light pulses  114  through a process called electro-luminescence. Details regarding embodiments of such LED devices are provided in above-cited Related application Ser. No. 12/584,904. 
         [0024]    Referring to  FIGS. 3A and 3B , application Ser. No. 12/584,904 discloses embodiments of an avalanche light emitting diode (ALED)  300  formed in a semiconductor substrate  302 , such as, for example, a silicon substrate or a gallium arsenide layer grown over a silicon substrate. An isolation ring  304  is formed within the substrate  302  to isolate additional structures that may be formed in the substrate  302  inside the isolation ring  304 . The isolation ring  304  may be a p+ ring that is formed utilizing multiple deep trenches formed in the substrate  302 . A p-type or n-type buried layer  306  is formed in the substrate  302  inside the isolation ring  304 . Various doped regions are formed in the substrate  302  inside the isolation ring  304  over the buried layer  306 . In the illustrated embodiment, the doped regions include doped regions  308  that are interleaved with doped regions  310 . The doped regions  308  and  310  have different dopant types. For example, doped regions  308  could be doped with P+ dopant and doped regions  310  could be doped with N+ dopant. In the illustrated embodiment, doped regions  308  and  310  are elongated regions that are arranged in generally vertical columns, with doped regions  108  being interleaved with doped regions  310 . A first polysilicon electrode  312  is electrically coupled to the doped regions  308  and a second polysilicon electrode  314  is electrically coupled to the doped regions  310 . Electrodes  312  and  314  include fingers that extend over the doped regions  308  and  310 , respectively. Vias  316  provide electrical connection between the electrodes  312  and  314  and the respective doped regions  308  and  310 . 
         [0025]    As shown in  FIG. 3B , the doped regions  308  and  310  are configured such that a tip  318  of a doped region  308  is generally positioned near a tip of a doped region  310 . Each of the tips  318 ,  320  is positioned at a point where two generally straight edges of a doped region meet. In the disclosed embodiment, a tip  318  of a doped region  308  represents the closest portion of that doped region  308  to a tip  310  of an adjacent doped region  310  in a local area or vice versa. The tips  318  and  320  may be separated by a distance of, for example, 0.05-0.15 μm. In this arrangement, the doped regions  308  and  310  are used to form multiple P-I-N structures, which are referred to as filaments  322 . The intrinsic or “I” regions of the filaments  322  represent lightly-doped regions of the substrate  302  between the doped regions  308  and  310 . Each filament represents an area where light can be generated when suitable voltages are applied to the electrodes  312  and  314 . 
         [0026]    Further details regarding embodiments of ALEDs may be obtained by reference to application Ser. No. 12/584,904. 
         [0027]    Dielectric Galvanic Isolation Barrier 
         [0028]    As discussed above, the one or more optical emitters, such as the ALEDS discussed above, are formed in the semiconductor substrate  106  as part of the first electrical system A and emit light pulses. This light is directed across a dielectric galvanic isolation barrier  108  to the second electrical system B, as shown in  FIG. 1 . 
         [0029]    In some embodiments, the dielectric galvanic isolation region  108  has two parts; a wide oxide filled trench created form the topside of the semiconductor substrate  106  and a backside trench. The topside oxide filled trench needs to be wide enough to ensure that it can handle a high voltage determined from the galvanic isolation specification. As discussed above, for individual components, this could be ˜5 kV, which would require a trench that is approximately 15 um wide. Standard trench fill process technology is not capable of filing a trench this wide with silicon oxide in a useable manner. Details regarding a method for forming an embodiment of a wide topside isolation trench are provided in above-cited Related application Ser. No. 12/315,934. 
         [0030]    application Ser. No. 12/315,934 discloses embodiments of high lateral voltage isolation structures and methods of forming such structures. According to methods disclosed therein, at least two trenches are formed in the topside of a semiconductor substrate around an active region, dielectric material (e.g., silicon oxide) is deposited in the trenches and any semiconductor material between the trenches is removed to define at least one additional trench. The initial trenches are typically formed in a manner known in the art, which may involve depositing on oxide-nitride stack to act as a hard mask, depositing photoresist over the hard mask, imaging the photoresist and then selectively etching the hard mask. Thereafter, the remaining photoresist is stripped away and the hard mask is used as a mask in etching the silicon to define the trenches. The etching of the silicon may be performed using a plasma etch that selectively etches silicon over oxide and nitride. The initial trenches are preferably etched down to a SOI layer and are typically 6 μm wide. The initial trenches may then be filled by growing a trench sidewall oxide and thereafter depositing dielectric (e.g., silicon dioxide) into the trench using chemical vapor deposition (CVD). Once the dielectric is deposited in the initial trenches, the dielectric material extending above the trenches is planaraized, e.g., by chemical mechanical polishing (CMP). Any remaining nitride hard mask material may then be removed using a nitride etch. The semiconductor material between the initial trenches is then removed by a masking and etching technique, which may include depositing a photoresist, imaging the photoresist and etching away at least the portion of the nitride-oxide hard mask that covers the semiconductor material that is to be removed, whereafter the photoresist is stripped away. The exposed semiconductor material may then be etched away utilizing a silicon etch, preferably down to the SOI layer to define at least one additional trench. The at least one additional trench may then be filled with dielectric (e.g., silicon dioxide) as part of a second CVD trench fill, thereby filling the region between the initial trenches to define one combined, wide trench. The dielectric material extending above the one or more additional trenches is typically planarized, e.g. by CMP. The semiconductor substrate  102  may therefore include a dielectric filled topside trench that is, for example, more than 15 μm wide. 
         [0031]    As shown in  FIG. 4 , the topside wide trench portion of the dielectric galvanic isolation barrier  108  is surrounded by metal  402  in order to direct as much of the light as possible that is generated by the optical emitters (e.g., LEDs)  404  in the direction of the optical receivers (photodiodes)  406 . Silicon dioxide is transparent to light so there should be minimal optical loss in the topside trench. As further shown in  FIG. 4 , the dielectric galvanic isolation barrier  108  also includes a backside trench  408  that is filled with dielectric material (e.g., SU8). 
         [0032]    Optical Receivers 
         [0033]    As shown in  FIG. 4 , on System B, the light from the LED crosses into a silicon photodiode  406  that acts as the optical receiver. The light within the photodiode generates electron-hole pairs which are then swept out of the device to sense circuitry. By modulating the LED power, it is therefore possible to transmit data across dielectric galvanic isolation barrier  108  to the photodiode receiver  406 . The signal from the photodiode  406  can be amplified and the data extracted and provided to the electrical circuitry  104  of system B ( FIG. 1 ). 
         [0034]    In a system B embodiment, by placing separate photodiodes radiating out from the LED, it is possible to detect different wavelengths of light. This is possible because light has an absorption coefficient that is dependent on wavelength. Longer wavelengths (e.g. green) will be detected further away compared with shorter wavelengths (e.g. red) which will be absorbed closer to the LED. By creating a series of LEDs, a spectrum of wavelengths may be detected. 
         [0035]    As stated above, the power for system B can be obtained from System A in accordance with galvanic isolation. A transformer may be used to pass power across from system A to the system B, as shown in  FIG. 5 . The transformer is designed to give high voltage protection by using thick inter-layer dielectrics. With a two layer Cu design of then type shown in the  FIG. 5  embodiment, the resistance can be reduced significantly and thereby give a high Q value at a high frequency (an example of this is Q ˜30 at 400 MHz). With such a high Q transformer, it is possible to design a resonant circuit that will allow power to be moved from system A to system B. By using a high frequency e.g. 400 MHz, the transformer size can be scaled down and thereby allow integration into a silicon system. 
         [0036]    When a light pulse is applied to a photodiode, carriers are generated very quickly (on the order of &lt;1 ns). However, when the light pulse is switched off, the photodiode requires a certain time to return to its off state. Typical times for this are in the &gt;1 us timescale for silicon devices and about 10-100× less in GaAs like devices. This is the limiting factor in the speed of the system and why opto-couplers are limited to only 1-1-0 MBps speeds. As stated above, in an embodiment of the invention, a refresh pulse is applied to the photodiode. This refresh pulse turns the diode on for a very short period of time, e.g. &lt;1 ns, which is enough to return the photodiode to its original state. This method allows the photodiode to operate in the GHz regime and &gt;100 Mbps for data transfer. The problem has been linking the clock for the refresh to the data transmitted by the LED. In an embodiment of the invention, the clock is transmitted across a transformer (or coupled inductor), but not necessarily the same transformer used for the resonant power transmission. 
         [0037]    It should be understood that the particular embodiments of the invention described above have been provided by way of example and that other modifications may occur to those skilled in the art without departing from the scope of the invention as expressed in the appended claims and their equivalents.