Patent Application
20120074818
1. Field
The present application relates to systems having integrated mechanical resonating structures, and related methods.
2. Related Art
Global positioning system (GPS) receivers utilize resonating elements to provide a reference signal. GPS receivers are sometimes used in combination with other devices that also utilize resonating elements. Conventionally, the resonating elements of the GPS receiver and any combined devices are not integrated.
According to one aspect, a system is provided, comprising a global positioning system (GPS) receiver having a first mechanical resonating structure, and an inertial navigation system (INS) comprising a second mechanical resonating structure. The first mechanical resonating structure and second mechanical resonating structure are integrated.
Further aspects are described below.
Various aspects and embodiments of the technology will be described with reference to the following figures. It should be appreciated that the figures are not necessarily drawn to scale. Items appearing in multiple ones of the figures are indicated by the same or a similar reference number in all the figures in which they appear.
Applicants describe herein devices and systems including two or more integrated mechanical resonating structures. In a non-limiting example, the mechanical resonating structures may be microelectromechanical (MEMS) resonating structures, and may be integrated either by being formed on separate semiconductor chips within a multi-chip module or by being formed on the same semiconductor chip (e.g., monolithically integrated). One of the mechanical resonating structures may be part of a GPS device (e.g., a GPS receiver) while a second one of the mechanical resonating structures may be part of a second device, such as an inertial navigation system (INS), a transceiver, or any other suitable device. One or more of the MEMS resonating structures may be piezoelectric.
According to one aspect of the technology, a GPS device (such as a GPS receiver) is coupled to a second device (such as an INS), and each includes one or more mechanical resonating structures. The mechanical resonating structures may perform any suitable functions, such as providing reference signals, operating as sensors (e.g., accelerometers, gyroscopes, pressure sensors, compasses, etc.), serving as filters (e.g., radio frequency (RF) filters, intermediate frequency (IF) filters, or any other suitable type of filters), or may serve any other function(s). Two or more of the mechanical resonating structures may be integrated, which may provide various benefits. According to a first non-limiting embodiment, the two or more mechanical resonating structures may be integrated within a multi-chip module, though they may be formed on separate semiconductor chips. According to an alternative, the integrated mechanical resonating structures may be formed on a single semiconductor substrate (e.g., monolithically integrated on the substrate). In one embodiment, the mechanical resonating structures may be formed on a single MEMS wafer and may be capped with a cap wafer which may or may not include circuitry to be coupled to the resonating structures.
According to another aspect of the technology, a system includes multiple MEMS components, one or more of which may be integrated with each other. In one non-limiting embodiment, the system may include a transceiver having numerous components, such as filters, switches, a GPS receiver, and an INS, or any other suitable components. Multiple ones of the components may be implemented as MEMS components, for example utilizing MEMS resonating structures. As a non-limiting example, a transceiver may include a MEMS-based filter, a MEMS-based switch, one or more MEMS reference clock generators, one or more accelerometers, one or more gyroscopes, or any other suitable components. Such components, conventionally formed and packaged as discrete components, may be integrated together, which may provide one or more of various benefits, such as space savings, improved performance, and ease of manufacturing, among others.
The aspects described above, as well as additional aspects, are described further below. These aspects may be used individually, all together, or in any combination of two or more, as the technology is not limited in this respect.
GPS devices, such as GPS receivers, are one example of devices which may include a mechanical resonating structure. For example, a mechanical resonating structure may be used as a reference oscillator or low frequency time reference to provide reference signals in the GPS receiver. An example is now described.
By way of explanation, the Global Positioning System is a space-based radio-navigation system that uses ranging signals broadcasted by multiple satellites to determine a precise position on or in proximity of the earth. Each satellite of the system continuously transmits a navigation message encoded at 50 bit/s and which contains three parts. The first part contains the GPS date and time (time-of-week and GPS week number) and the satellite's health status. The second part comprises high precision orbital information of the satellite referred to as ephemeris data. The third part contains the almanac data that contains information on coarse orbit and status of all satellites in the constellation, an ionospheric model, and the relationship of GPS derived time and Coordinated Universal Time (UTC).
Each satellite of the GPS system broadcasts signals using the two carrier frequencies 1575.42 MHz, also referred to as L1 frequency, and 1227.60 MHz, referred to as L2 frequency. Multiple frequencies are used for multiple reasons, including redundancy, resistance to jamming, and ability to measure the ionospheric delay error. A GPS system might use one, two, or more frequencies and it should be understood that the various aspects described herein applying to GPS receivers are not limited to using any particular number of frequencies.
To distinguish signals from different satellites despite the signals being sent on the same carrier frequency (e.g., the L1 carrier frequency) the GPS system uses a code division multiple access (CDMA) spread-spectrum technique. The navigation message, described above, is encoded with a 1023 bit long pseudo random (PRN) sequence that is unique for each satellite. This CDMA encoding is often referred to as coarse/acquisition code (C/A) or Gold code. The 1023 bit C/A sequence has a period of 1 millisecond and is transmitted continuously. Only 32 combinations of all possible combinations from the 1023 bit long code are used, and each satellite in the GPS system uses one unique code. Currently, only the L1 carrier is modulated with the C/A code, but additional frequencies may become available for civil applications in the future and it should be understood that those aspects described herein relating to GPS receivers are not limited to GPS receivers using any specific number of carrier frequencies. In addition to C/A code, a high precision military CDMA code (so-called P code) exists, which is not described in detail here.
The 1575.42 MHz carrier frequency (L1) is generated by an atomic clock in each satellite, providing utmost stability and accuracy. Large frequency fluctuations of the carrier frequency affect the achievable accuracy of the position computed by a GPS receiver based on the satellite ranging signal, and further affect the time it takes to compute a valid position, as well as influencing the critical signal level necessary to obtain a position estimate. The use of highly precise atomic clocks in the satellites minimizes these effects.
For a GPS receiver to obtain a position based on the received ranging signals of multiple satellites, the actual ranging signal has to be demodulated from the carrier. This demodulation requires a reference frequency on the receiver side to down-convert the GPS signal. A block diagram of a GPS receiver 100 is shown in
The carrier frequency tracking loop of a receiver channel 120 uses a phase locked loop (PLL) to lock a numerically controlled oscillator (NCO) to the digital IF signals from ADC 118 for a particular satellite, or rather to the satellite's C/A code. The frequency tracked by the PLL (fPLL) incorporates any frequency variation of the satellite carrier due to Doppler shifts, fluctuations of the satellite's time base, frequency inaccuracies and drift of the local reference oscillator 106 introduced during the down-conversion by down-converter 114 and the analog-to-digital sampling process of ADC 118.
The code tracking loop of receiver channel 120 uses a delay-lock loop (DLL) to track the C/A code of the respective satellite for each receiver channel. The DLL uses the carrier replica signal from the NCO of the carrier frequency tracking loop. Tracking the delay of the C/A code in the DLL yields information about the time delay between the satellite and the receiver, basically by measuring the offset between the received PRN sequence and the internally generated 1023 bit C/A code replica. In combination with knowledge of the precise satellite time and position, the range of the GPS receiver from the satellite can be estimated. As the PRN code is transmitted over a period of 1 ms, one bit corresponds to 0.98 microseconds (10−3 s/1023), which, assuming the propagation of the satellite signal at the speed of light (299 792 458 m/s), corresponds to a distance of 293 meters. Currently available GPS receivers are able to detect the offset of rising and trailing edges of each bit to about 1% accuracy, which reduces the location uncertainty of 293 meters to less than 3 meters. The ranges for the satellite determined from the code tracking loop are referred to as pseudoranges. The expression of pseudorange refers to the range estimates being affected by a common offset. The delay obtained from the DLL tracking is affected by the clock error of the reference (or “local”) oscillator. Because the clock error is assumed to be constant over a short period of time, the error of the range estimates is assumed to be constant.
The receiver processor 122 in
The accuracy of the frequency fPLL tracked by the GPS carrier frequency tracking loop is affected by the GPS carrier-to-noise (C/N) ratio (white noise phase jitter), satellite clock phase jitter, receiver clock phase jitter, vibration-induced phase jitter, atmospheric phase jitter (all colored noise phase jitter), and dynamic stress due to sudden movement of the receiver. Depending on the application, the receiver clock phase jitter may be one of the most dominating effects.
The accuracy and stability of the frequency fPLL determines the accuracy of the resulting calculated position of the GPS receiver and the robustness of the GPS receiver operation for very low C/N ratios. Robustness against cycle slip of the carrier tracking loop may impact performance of the GPS receiver, for example influencing the ability of the GPS receiver to maintain lock on the GPS carrier. Cycle slip can occur for numerous reasons including weak GPS signal strength (for example as may occur inside buildings, caves, and obstructions), strong phase fluctuations of the GPS signal (for example as may result from ionospheric fluctuations/scintillation effects, multi-path reflections in urban environment, etc.), dynamic stress, or any instability or malfunction of the satellite or receiver.
Conventionally, GPS receivers use temperature compensated crystal oscillators (TCXOs) or, for higher performance, oven controlled crystal oscillators (OCXOs) as the reference oscillator (e.g., as reference oscillator 106 in
GPS devices may be used in combination with other devices. For example, GPS devices may be used in combination with other devices which augment the location determination functionality of the GPS devices, as a non-limiting example. As mentioned, GPS signal quality and strength, and therefore the performance of GPS receivers, is negatively impacted by multiple factors. Those factors include some weather conditions, attenuation of the GPS signals by buildings and objects, and multi-path signals and multi-path fading encountered in urban environments. Some such factors result in weak GPS signals or GPS signal outages, which cause inaccurate position readings from the GPS receivers. In addition, current GPS receivers require a long time to establish an initial position (referred to as “Time To First Fix” (TTFF)) and subsequent positions (referred to as “Time To Subsequent Fix” (TTSF)), which times are also extended by weak GPS signals and GPS signal outages. This limits the use of GPS in urban environments, buildings, tunnels, caves and under water.
One manner of addressing the shortcomings of GPS receivers in determining location is to use an integrated navigation system which augments the GPS data with data that is not susceptible to the same limitations as GPS data (e.g., augmenting GPS data with a complementary navigation system that can work in any environment, even those characterized by GPS signal outages). An inertial navigation system (INS) is an example of a suitable complementary navigation system.
Inertial navigation systems use inertial sensors such as accelerometers and gyroscopes to track the position and orientation of an object with respect to a reference point. The linear acceleration and rotation rate information provided by accelerometers and gyroscopes are integrated over time to deliver position and orientation information compared to the reference point, a technique referred to as Dead Reckoning (DR). A typical DR configuration may include one gyroscope for direction measurements and a 3-axis accelerometer, though other configurations are also possible. A magnetometer may also be included. INS can be used as a self-contained system without dependency on transmission and reception of external electrical signals, and may also be used as an assistance positioning system together with a global positioning system (GPS) device which provides location information. For example, the INS may provide location and orientation relative to the last valid GPS data point (i.e., the last valid GPS-determined location may serve as the reference point for the INS).
Even though integrated navigation systems combining GPS and DR techniques are already in use in some applications, such integrated navigation systems are not available for mass market portable consumer devices such as cellular phones, since no integrated navigation system combining GPS with an INS satisfies the basic preferences of light weight, small footprint, low power consumption and low cost associated with mass market portable consumer devices. Thus, currently, in most portable or handheld navigation devices, position is determined using only GPS data.
According to one aspect, an integrated system including a GPS device and an INS is described. The GPS and INS may be integrated on the same chip. The system may include MEMS-based components. For example, in some embodiments, the GPS device may include a MEMS-based reference oscillator, and the INS may include a MEMS-based gyroscope and a MEMS-based accelerometer. The MEMS-based gyroscope may be a single-axis or multi-axis MEMS gyroscope. The MEMS-based accelerometer may be a single-axis or multi-axis accelerometer.
In some embodiments, the GPS device includes one or more MEMS-based timing oscillators. For example, the timing oscillator may be a TCMO (temperature-compensated MEMS oscillator) and/or an OCMO (oven-controlled MEMS oscillator). Suitable timing oscillators have been described, for example, in: U.S. patent application Ser. No. 12/830,056, entitled “Methods and Apparatus for Tuning Devices Having Resonators”, filed Jul. 2, 2010 under Attorney Docket No. G0766.70019US00 and published as U.S. Patent Publication No. US-2010-0315170; U.S. Patent Application Ser. No. 61/363,759, entitled “Methods and Apparatus for Calibration and Temperature Compensation of Oscillators Having Mechanical Resonators”, filed Jul. 13, 2010 under Attorney Docket No. G0766.70021US00; and U.S. patent application Ser. No. 12/639,161 filed on Dec. 16, 2009 under Attorney Docket No. G0766.70006US01, entitled Mechanical Resonating Structures Including A Temperature Compensation Structure, and published as U.S. Patent Application Publication No. US-2010-0182102-A1 on Jul. 22, 2010, all of which are incorporated herein by reference in their entireties.
In operation, the 3-axis gyroscope 206 and 3-axis accelerometer 208 provide their output signals to the INS processor 210. The INS processor 210 processes the received gyroscope and accelerometer signals to determine the position and orientation of the system 200 relative to a reference point (i.e., the changes in position and orientation). The position and orientation calculated by the INS processor 210 may be provided as output signal 211. The GPS device 204 provides an output signal 205 representing a GPS location.
The system 200 further comprises a GPS-INS processor 216 which processes the GPS data from the GPS device 204 (in the form of signal 205) and the output of the position and orientation data from the INS processor 210 (in the form of signal 211) to determine one or more of the absolute position (location), velocity, and altitude of the system 200, one or more of which quantities may then be provided by the GPS-INS processor 216 as an output signal 218.
According to one aspect of the technology, one or more mechanical resonating structures of an integrated navigation system, such as system 200 of
The integration of the mechanical resonating structures of an integrated navigation system may be performed in any suitable manner. To aid the understanding of the possibilities, a non-limiting example of a mechanical resonating structure is now described with respect to
The micromechanical resonating structure 310 also includes a silicon layer 312, a silicon oxide layer 314 on the top surface of the silicon layer 312, and a silicon oxide layer 316 on the bottom surface of the silicon layer 312. The combination of silicon layer 312 and silicon oxide layers 314 and 316 may operate as a temperature compensation structure (a temperature compensation stack in this configuration) to compensate temperature-induced changes in the frequency of operation of mechanical resonating structure 310. For example, one manner in which to improve the temperature drift of silicon resonators is to add another layer of material on the silicon that, instead of softening with temperature, as is the case for silicon, hardens with temperature, as is the case for quartz and silicon dioxide. As disclosed in U.S. patent application Ser. No. 12/639,161 filed on Dec. 16, 2009 under Attorney Docket No. G0766.70006US01, entitled MECHANICAL RESONATING STRUCTURES INCLUDING A TEMPERATURE COMPENSATION STRUCTURE, and published as U.S. Patent Application Publication No. US-2010-0182102-A1 on Jul. 22, 2010, incorporated herein by reference in its entirety, a stack of two silicon oxide layers on the top and bottom of the silicon, respectively, can be implemented with a piezoelectric stack on either the top or bottom oxide (see, for example,
The micromechanical resonating structure may be connected to a substrate 302 by two or more anchors. As shown in
As mentioned, various types and forms of mechanical resonating structures may be used with those aspects of the present technology relating to mechanical resonating structures, and
The mechanical resonating structure may have any shape, as the shape illustrated in
The mechanical resonating structures described herein may have any suitable dimensions, and in some embodiments may be micromechanical resonating structures. The mechanical resonating structure may have any suitable thickness, and in some embodiments the thickness may be related to a wavelength of a desired oscillation mode.
According to some embodiments, the mechanical resonating structures described herein have a large dimension (e.g., the largest of length, width, diameter, circumference, etc. of the mechanical resonating structure) of less than approximately 1000 microns, less than approximately 100 microns, less than approximately 50 microns, or any other suitable value. It should be appreciated that other sizes are also possible. According to some embodiments, the devices described herein form part or all of a microelectromechanical system (MEMS).
The mechanical resonating structures may have any desired resonance frequencies and frequencies of operation, and may be configured to provide output signals of any desired frequencies. For example, the resonance frequencies and/or frequencies of operation of the mechanical resonating structures, and the frequencies of the output signals provided by the mechanical resonating structures, may be between 1 kHz and 10 GHz. In some embodiments, they may be in the upper MHz range (e.g., greater than 100 MHz), or at least 1 GHz (e.g., between 1 GHz and 10 GHz). In some embodiments, they may be at least 1 MHz (e.g., 13 MHz, 26 MHz) or, in some cases, at least 32 kHz. In some embodiments, they may be in the range of 30 to 35 kHz, 60 to 70 kHz, 10 MHz to 1 GHz, 1 GHz to 3 GHz, 3 GHz to 10 GHz, or any other suitable frequencies. Thus, it should be appreciated that the listed frequencies are not limiting.
The mechanical resonating structures may be operated in various acoustic modes, including but not limited to Lamb waves, also referred to as plate waves including flexural modes, bulk acoustic waves, surface acoustic waves, extensional modes, translational modes and torsional modes. The selected mode may depend on a desired application of the mechanical resonating structure.
The mechanical resonating structure may be actuated and/or detected in any suitable manner, with the particular type of actuation and/or detection depending on the type of mechanical resonating structure, the desired operating characteristics (e.g., desired mode of operation, frequency of operation, etc.), or any other suitable criteria. For example, suitable actuation and/or detection techniques include, but are not limited to, piezoelectric techniques, electrostatic techniques, magnetic techniques, thermal techniques, piezoresistive techniques, any combination of those techniques listed, or any other suitable techniques. The various aspects of the technology described herein are not limited to the manner of actuation and/or detection.
According to some embodiments, the mechanical resonating structures described herein may be piezoelectric Lamb wave devices, such as piezoelectric Lamb wave resonators. Such Lamb wave devices may operate based on propagating acoustic waves, with the edges of the structure serving as reflectors for the waves. For such devices, the spacing between the edges of the resonating structure may define the resonance cavity, and resonance may be achieved when the cavity is an integer multiple of pitch p, where p=λ/2, with λ being the acoustic wavelength of the Lamb wave of interest, understanding that the device may support more than one mode of Lamb waves. However, it should be appreciated that aspects of the technology described herein apply to other types of structures as well, and that Lamb wave structures are merely non-limiting examples.
As should be appreciated from
As mentioned, the mechanical resonating structures of the system 200 of
As shown, the multi-chip module 400 includes chips 402 and 404, on which mechanical resonating structures 406 and 408 are formed, respectively. The chips 402 and 404 may be semiconductor chips, for example being semiconductor substrates (e.g., silicon substrates, though other materials are also possible). The chips 402 and 404 may include circuitry for connecting to the mechanical resonating structures 406 and 408. Mechanical resonating structures 406 and 408 may form any suitable components of an integrated navigation system. For example, mechanical resonating structure 406 may form at least part of a timing oscillator of a GPS receiver, for example providing a reference clock signal for the GPS receiver. Mechanical resonating structure 408 may form at least part of a 3-axis accelerometer for an INS. However, these are non-limiting examples, as it should be appreciated that the mechanical resonating structures 406 and 408 may form any suitable components of an integrated navigation system.
The multi-chip module 400 further comprises a package 410 in which the chips 402 and 404 are placed. The package may be any suitable package, including a plastic or ceramic package, as non-limiting examples. The package may have any suitable height and the mechanical resonating structures 406 and 408 may have dimensions which facilitate their placement within the package, for example having any of the dimensions previously listed herein with respect to
It should be appreciated that
In an alternative embodiment, two or more of the mechanical resonating structures of the system 200 may be integrated on the same semiconductor chip, for example being monolithically integrated. In some cases, it is preferred to integrate all the subcomponents of an integrated navigation system on a single chip. One manner in which such monolithic integration of multiple components of an integrated navigation system (or other system) may be accomplished is via the formation of membranes in a semiconductor substrate, with different membranes being incorporated into different mechanical resonating structures, as described in U.S. patent application Ser. No. 13/112,587, filed May 20, 2011 under Attorney Docket No. G0766.70020US01, and entitled “Micromechanical Membranes and Related Structures and Methods”, which is hereby incorporated herein by reference in its entirety. A non-limiting explanation is now provided.
Applicants have appreciated that silicon membranes suitable for forming micromechanical resonating structures may be formed using empty-space-in-silicon (ESS) principles, and furthermore that oxidation of such silicon membranes may then be performed to form temperature compensated structures. Thus, according to one aspect of the technology, silicon membranes suitable for formation of micromechanical resonating structures are formed from a silicon substrate. The dimensions of the membranes (e.g., thickness and area) may be selected to facilitate subsequent formation of a mechanical resonating structure having desired vibratory characteristics. The silicon membranes may be formed using ESS principles, as will be further described below, and in some embodiments may be oxidized to form temperature-compensated structures.
Applicants have further appreciated that ESS principles may be used to form multiple silicon membranes on the same silicon substrate, which may be used to form distinct micromechanical resonating structures, for instance to be used in different MEMS devices. Moreover, Applicants have appreciated that it may be beneficial in some instances to form, on the same substrate, silicon membranes of different thicknesses and/or with different oxide configurations, for example to provide devices incorporating such structures with different mechanical properties (e.g., vibratory properties).
Thus, according to another aspect of the technology, two or more silicon membranes are formed on the same silicon substrate and differ in one or more respects which may impact the vibratory characteristics of the membranes and thus the vibratory characteristics of resonating structures formed from the membranes. According to one such aspect, two or more of the silicon membranes may differ in their thicknesses, which therefore may result in the membranes exhibiting different vibratory characteristics. According to another such aspect, differing oxide configurations may be formed with respect to two or more of the silicon membranes. The oxide configurations may differ in terms of the presence or absence of oxide, the location of oxide, and/or the thickness of oxide.
According to another aspect of the technology, multiple silicon membranes are formed on a silicon substrate using different trench patterns in conjunction with ESS principles. The trench patterns may differ in terms of the area of the openings of the trenches, the depths of the trenches, the aspect ratios of the trenches and/or the pitches of the trench patterns. Annealing of the silicon substrate after formation of the trenches may then result in silicon membranes of differing dimensions (e.g., different thicknesses), as a result of the differing trench patterns.
As mentioned, according to the present aspect, the membrane 514 may be suitable for formation of a mechanical resonating structure (e.g., by defining such a structure from the membrane), by proper shaping and dimensioning of the membrane. As shown in
According to one non-limiting embodiment, to provide suitable vibratory characteristics, the membrane thickness T may be between approximately 1 and 20 microns. According to another embodiment, T may be between approximately 1 and 10 microns (e.g., 2 microns, 5 microns, etc.). According to one embodiment, T may be less than approximately three wavelengths of a resonance frequency of interest of a mechanical resonating structure to be formed from the membrane. According to some embodiments, the thickness T is less than approximately two wavelengths of a resonance frequency of interest of a resonating structure to be formed from the membrane. In still other embodiments, the thickness T may be less than approximately one wavelength of a resonance frequency of interest (e.g., less than approximately one wavelength of a resonant Lamb wave supported by a mechanical resonating structure to be formed from the membrane). Thus, it should be appreciated that the thickness of the membrane may determine or depend on the types of waves to be supported by a resonating structure to be formed from the membrane. For example, a given thickness may limit the ability of the resonating structure to support Lamb waves, or certain modes of Lamb waves. Thus, the thickness may be chosen dependent on the types and/or modes of waves desired to be supported by a mechanical resonating structure to be formed from the membrane. According to any of those embodiments described above, the thickness T may be substantially uniform (as shown in
According to one embodiment, suitable vibratory characteristics of the membrane 514 may be provided by suitably selecting not only the thickness of the membrane, but also at least one other dimension (e.g., length or width) of the membrane. For instance, suitable selection of the ratio of the thickness (T) to the maximum dimension of L and W (i.e., the larger of L and W) may provide suitable vibratory characteristics of the membrane such that the membrane is suitable for formation of a mechanical resonating structure (e.g., a micromechanical resonating structure to be used in a MEMS oscillator). According to one non-limiting embodiment, the ratio of T to the larger of L and W is between 1:20 and 1:500 (e.g., 1:100, 1:200, 1:300, 1:400, etc.). According to an alternative embodiment, the ratio of T to the larger of L and W is between 1:20 and 1:100 (e.g., 1:20, 1:50, etc.). It should be appreciated that other ratios are also possible, and that those listed are provided for purposes of illustration and not limitation. It should also be appreciated that the rectangular shape of the membrane 514 illustrated in
In any of those embodiments described above, or any other embodiments described herein in which the membrane has a length (L) and width (W), L and W may have any suitable values. For example, one or both of L and W may be less than approximately 1000 microns, less than approximately 100 microns (e.g., 75 microns, 60 microns, 50 microns, 40 microns, or any other value within this range), between approximately 50 microns and 200 microns, between approximately 70 microns and 120 microns, between approximately 30 microns and 400 microns, or have any other suitable values. Also, L and W need not be the same, and may differ by any suitable amounts, as the various aspects described herein as relating to membranes having dimensions L and W are not limited in this respect. According to some embodiments, L and W may be selected such that the area A is between approximately 110% and 300% (e.g., approximately 120%, approximately 150%, approximately 230%, approximately 250%, etc.) of the area of a mechanical resonating structure to be formed from the membrane, or in other embodiments between approximately 110% and 200% of the area of a mechanical resonating structure to be formed from the membrane, as described below.
According to one aspect of the technology, a membrane (e.g., a single crystal silicon membrane) formed on a substrate (e.g., a single crystal silicon substrate) and suitable for formation of a mechanical resonating structure (e.g., a micromechanical resonating structure) is oxidized to provide a temperature compensated structure of the type(s) previously described with respect to U.S. patent application Ser. No. 12/639,161 (i.e., including silicon sandwiched between two layers of silicon oxide). A non-limiting example is illustrated in
The illustrated apparatus 600 is similar to the apparatus 500 of
The access holes may be of any suitable number and positioning, as well as each having any suitable size and shape, to facilitate formation of a desired oxide configuration (e.g., oxidizing the cavity 512 and/or the bottom of the membrane 514).
To form the oxide illustrated in
As mentioned, the formation of the SiO2—Si—SiO2 multi-layer structure of apparatus 600 may provide temperature compensated functionality. Suitable selection of the ratio of the thickness of the silicon membrane to the total thickness of the silicon oxide layer(s) (e.g., the combined thickness of oxide layers on the top and bottom surfaces of the membrane) may provide for temperature compensation of a desired acoustic mode of vibration for a resonating structure formed from the membrane. For example, the ratio of the total thickness of the silicon oxide on the top and bottom surfaces of the membrane (when oxide is present on both the top and bottom surfaces of the membrane) to the silicon of the membrane may be between 1:0.1 and 1:10, between 1:0.5 and 1:3, between 1:0.75 and 1:1.25, or between 1:1 and 1:2, among other possible ratios. Thus, suitable values of the thickness of the oxide layer(s) may be determined from these ratios by reference to the suitable values of the thickness T of the membrane, described above.
Utilizing ESS principles with a subsequent oxidation step to form the oxidized structure illustrated in
As mentioned, membranes of the type described herein may be utilized to form a mechanical resonating structure that may serve as part or all of a MEMS device, such as a MEMS oscillator. A non-limiting example is the mechanical resonating structure 310 of
It should be appreciated that those mechanical resonating structures described herein as being formed from membranes may have any suitable dimensions, and in some embodiments may have a thickness corresponding to the thickness of a membrane (plus any oxidation layers on the membrane) from which the mechanical resonating structure is defined.
As mentioned, Applicants have appreciated that in some instances it may be beneficial to form two or more membranes (e.g., single crystal silicon membranes) on the same substrate, such that the membranes may be incorporated into different devices (e.g., distinct oscillators). In some embodiments, the membranes may have different vibratory characteristics, such that the devices incorporating the membranes may have different vibratory characteristics, though in other embodiments multiple ones of the membranes may have substantially the same vibratory characteristics. Thus, according to another aspect, two or more silicon membranes may be formed on a silicon substrate, with the membranes differing in thickness. According to yet another aspect, two or more silicon membranes may be formed on a silicon substrate and differing oxide configurations may be formed with respect to the silicon membranes, such that differing mechanical characteristics may be provided.
As shown, at least two of the membranes (e.g., membranes 704a and 704d) may have differing thicknesses, and may furthermore have differing areas, although not all embodiments are limited in this respect. The differing thicknesses may result in the membranes exhibiting different vibratory characteristics, which may lead to differing behavior of mechanical resonating structures formed from the different membranes. Thus, the thickness of each membrane may be selected to provide desired vibratory characteristics, and the differences in thickness may therefore depend on the differences in desired vibratory characteristics. According to one embodiment, a thickness of one membrane may differ from a thickness of a second membrane by between approximately 1 micron and 20 microns (e.g., 2 microns, 5 microns, 10 microns, etc.). According to another embodiment, a thickness difference of two membranes may be between approximately 1 micron and 10 microns, and according to a further embodiment the difference may be between approximately 3 and 10 microns. However, it should be appreciated that other difference values may alternatively be used and that those listed are non-limiting examples.
An apparatus including multiple silicon membranes of differing thicknesses, such as apparatus 700 of
As shown, the apparatus 800 in this non-limiting example includes a substrate 802 (e.g., a silicon substrate or any other type of substrate described herein) with four distinct trench patterns, 804a-804d, each of which is a one dimensional trench pattern (as will be seen and described further with respect to
In the non-limiting example of
In the non-limiting example of
As shown in
According to one embodiment, multiple one-dimensional trench patterns are formed in a substrate, with each being suitable to form a membrane. At least some trenches of a first pattern have a first opening area and a first depth. At least some of the trenches of the first pattern are spaced by a first pitch. At least some trenches of a second pattern have a second opening area and a second depth, and at least some of the trenches of the second pattern are spaced by a second pitch. According to one embodiment, at least one of the following conditions is met: (a) the first depth differs from the second depth; (b) the first opening area differs from the second opening area; and (c) the first pitch differs from the second pitch.
Thus, it should be appreciated that
As can be seen from
The trenches may be formed using various anisotropic dry etching techniques, including, but not limited to, deep reactive ion etching (DRIE), which is often used in combination with a cyclic passivation deposition (the combination being referred to as Bosch process or advanced silicon etch (ASE)). Alternatively, the trenches may also be formed by anisotropic wet etching techniques, including KOH, EDP and TMAH based etch chemistries as well as anodization based etch techniques. Depending on the parameters, i.e. the current density during the anodization process, the silicon might not be completely etched. It should be understood that in some cases the trenches will contain porous silicon residue.
As mentioned, the resulting apparatus (e.g., apparatus 800 of
Thus, according to one embodiment, different mechanical resonating structures of a system may be monolithically integrated on the same semiconductor chip using the techniques described above for forming multiple membranes on a semiconductor substrate. As explained, the membranes may be formed with the same or different dimension. According to one embodiment, membranes of different thicknesses may be formed, and may thus be used to form monolithically integrated mechanical resonating structures of different thicknesses. As a non-limiting example, a first membrane may be used to form a gyroscope (e.g., a multi-axis gyroscope, such as a 3-axis gyroscope) while a second membrane may be used to form an accelerometer (e.g., a multi-axis accelerometer, such as a 3-axis accelerometer). Typically, gyroscopes require greater mass than that required for an accelerometer. For instance, a MEMS gyroscope may be on the order of 500 micron thick, while a MEMS accelerometer may be on the order of 100 micron, as non-limiting examples. Thus, according to one non-limiting embodiment, the first membrane may be thicker than the second membrane. Other configurations are also possible. A non-limiting example is shown in
The device 900 includes two mechanical resonating structures monolithically integrated with a substrate 902 (e.g., a silicon substrate). The mechanical resonating structures 904 and 906 may be formed using the techniques described herein for forming membranes, or may be formed in any other suitable manner. As shown, the mechanical resonating structure 904 may have a thickness T904 greater than a thickness T906 of the mechanical resonating structure 906. Such differences in thickness may be used for any suitable purpose, for example, to form different mechanical resonating structures have different vibratory characteristics.
A integrated navigation system, such as system 200, in which one or more of the components is integrated (for example, one or more of the mechanical resonating structures is integrated) may provide various benefits. Non-limiting examples of benefits which may be realized according to one or more embodiments include an integrated navigation system that is self-contained and may not need to rely on other external aids. The error rate of the GPS device may be reduced by integration of the INS and the GPS information. The system may provide position, velocity, and/or altitude data in real time at high data rates. The integration of components may allow the system size and power consumption to be reduced compared to conventional systems. Cost reduction may also be achieved. Such benefits may allow the systems to be used in hand-held devices such as cellular phone and GPS systems, consumer electronics (digital cameras, gaming consoles, smart phones, household appliances), robots, automobiles (e.g., for ride stabilization and roll over detection), space and military applications, and aerospace and navigations systems, among others. The integration of components of the system may also enhance the system's robustness.
As has been explained above, according to some embodiments multiple structures (e.g., multiple MEMS structures, such as multiple mechanical resonating structures) may be formed on a single substrate. In some instances, the substrate may include circuitry coupled to the structures, for example drive and sense circuitry coupled to a mechanical resonating structure configured as an oscillator. According to some embodiments, a substrate or wafer including multiple mechanical resonating structures, which may be referred to as a “device wafer”, may be bonded to another substrate or wafer acting as a cover (also referred to herein as a cap). In some such embodiments, the cap wafer may include circuitry (e.g., integrated circuitry) that is coupled to the mechanical structures on the device wafer. In some embodiments, a MEMS wafer includes multiple mechanical resonating structures and a cap wafer that includes integrated circuitry to control the mechanical resonating structures is bonded to the MEMS wafer. Non-limiting suitable configurations and processes for bonding a device wafer to a cap wafer (e.g., for forming capped wafers, including processes for wafer-level packaging techniques and IC-to-MEMS bonding) have been described, for example, in: U.S. patent application Ser. No. 12/750,768, filed Mar. 31, 2010 under Attorney Docket No. G0766.70009US01, entitled “Integration of Piezoelectric Materials with Substrates” and published as U.S. Patent Publication No. 2010-0301703; U.S. patent application Ser. No. 12/899,447, filed Oct. 6, 2010 under Attorney Docket No. G0766.70026US00, and entitled “Integration of Piezoelectric Materials with Substrates”; and U.S. Patent Application Publication No. 2009-0243747, all of which are incorporated herein by reference in their entireties.
A non-limiting example of a device wafer bonded to a cap wafer is now explained with respect to
The mechanical resonating structure 1002 may be any type of mechanical resonating structure, such as any of those types previously described herein. According to some embodiments, the mechanical resonating structure 1002 may be piezoelectrically actuated using resonant modes that do not require vacuum. These modes may have minimal, or no, out of plane movement that would be damped by the presence of gas pressure so no cavity is required in a wafer that is stacked above the device (MEMS) wafer. Because such mechanical resonating structures can function in a clean air environment and do not require an etched cavity cap, any wafer containing such mechanical resonating structures may be bonded directly to other wafers such as complementary metal oxide semiconductor (CMOS) wafers to create ultra-small form factor, low cost MEMS devices. Thus, according to some embodiments, the substrate 1008 may be attached to a CMOS wafer. The resulting devices may be very thin and have high yields.
In general, the attachment of the device wafer to a cap wafer may be done in any suitable manner, for example using a eutectic bond. This bond can be done with commonly available metals such as gold, tin, aluminum, copper, molybdenum, nickel, germanium or combinations of the aforementioned. This metal can also be used to create interconnects amongst and between the die. It can also be used to create metal structures such as high-Q inductors. Through silicon vias can be used in either wafer (the device wafer or cap wafer) to route the signal out of the device. The types of wafers which may be used as cap wafers can include a CMOS IC wafer, SiGe BiCMOS wafer, Gallium Arsenide wafer or others.
In general, the techniques described herein can be used to create many MEMS devices such as oscillators, radio frequency (RF) filters, gyroscopes, accelerometers, pressure sensors and switches. MEMS devices have been described, for example, in U.S. Patent Application Publication No. US-2009-0267699, entitled “Timing Oscillators and Related Methods”, U.S. patent application Ser. No. 12/830,056, entitled “Methods and Apparatus for Tuning Devices Having Resonators”, filed Jul. 2, 2010, and U.S. Patent Application Ser. No. Ser. No. 61/363,759, entitled “Methods and Apparatus for Calibration and Temperature Compensation of Oscillators Having Mechanical Resonators”, filed Jul. 13, 2010, all of which are incorporated herein by reference in their entireties.
Returning to
As mentioned, mechanical resonating structures or other components according to the aspects described herein may be coupled to circuitry (e.g., integrated circuitry) on the substrate(s). The circuitry may control operation of the structures (e.g., may actuate a piezoelectric material structure), may detect operation of the structures (e.g., may detect vibration of the mechanical resonating structure 1002), may process input and output signals sent to/from the structures, or may perform any other suitable functions. In situations in which multiple MEMS structures (e.g., mechanical resonating structures) are formed on a same substrate, each may have its own dedicated circuitry, whether formed on the same substrate as the structures, on a cap wafer, or in any other suitable location. According to one embodiment, multiple mechanical resonating structures are monolithically integrated on a device wafer, and integrated circuitry is also on the device wafer. Alternatively, multiple MEMS structures may share circuitry, whether on the same substrate as the structures, on a cap wafer, or in any other suitable location.
In device 1000, several components provide electrical access to the mechanical resonating structure 1002. Access may be provided to circuitry on the substrate 1008, circuitry on the cap 1010 (if any), and/or circuitry external to the device 1000. For example, in addition to providing bonding, the metallization layer 1012 may also provide electrical connection to the resonating structure 1002, and in particular to the electrode 1006. The metallization layer 1012 may therefore provide an electrical path to circuitry on substrate 1008 and/or circuitry on cap 1010. According to an alternative embodiment, the metallization layer 1012 may operate to provide a hermetic seal, and internal connections (internal to the perimeter of metallization 1012) may be used to provide electrical connection between an IC and a MEMS. According to the non-limiting embodiment of
The device 1000 further comprises additional layers 1016, 1018, and 1020. Layer 1016 may be an insulation layer (e.g., SiO2), formed in any suitable manner (e.g., deposition or growth), and etched in any suitable manner for subsequent formation of layers 1018 and 1020. The layers 1018 and 1020 may represent under-bump metallization (UBM) to provide electrical access to the mechanical resonating structure and/or integrated circuitry of device 1000 from the backside of the substrate 1008, and thus may be formed of any suitable materials and in any suitable manner. For example, the layer 1018 may be electroless plated nickel and the layer 1020 may be electroless plated gold, although other materials and methods of formation are also possible.
Various non-limiting examples of devices forming an integrated navigation system have been described. However, it should be appreciated that the various aspects described herein are not limited to such devices. For instance, according to one embodiment, an integrated navigation system may form part of a larger device or system. An example is now described in connection with
A transceiver is a device that has both a transmitter and a receiver which can be combined and share common circuitry. Transceiver functionality (receive and transmit) in each frequency band may require a number of discrete components positioned prior to digitization of the received signal. The number of discrete transceiver components continues to rise as more frequency bands and functionalities are added to transceivers.
Conventional transceiver components are discrete components. Thus, as the number of components continues to rise, the size and complexity of manufacturing transceivers rises as well. According to an aspect of the technology, a transceiver includes one or more MEMS components which are integrated, for instance in the manners previously described herein. Such integration may facilitate space savings and ease of fabrication of a transceiver, and may also improve the robustness of the transceiver.
As shown in
The transceiver 1100 illustrated in
As should be appreciated from the previous discussion of
Thus, it should be appreciated that a transceiver architecture that includes integrated MEMS-based components has been described. The MEMS-based components may be integrated on a single chip. The components may be RF components. Replacement of off-chip discrete components in certain conventional transceiver architectures by on-chip MEMS components may allow for the reduction of system size and power consumption, which may improve functionality, reduce cost and enhance robustness, amongst other advantages.
The mechanical resonating structures described herein may be used as stand-alone components, or may be incorporated into various types of larger devices. Thus, the various structures and methods described herein are not limited to being used in any particular environment or device. However, examples of devices which may incorporate one or more of the structures and/or methods described herein include, but are not limited to, tunable meters, mass sensors, gyroscopes, accelerometers, switches, and electromagnetic fuel sensors. According to some embodiments, the mechanical resonating structures described are integrated in a timing oscillator. Timing oscillators are used in devices including digital clocks, radios, computers, oscilloscopes, signal generators, and cell phones, for example to provide precise clock signals to facilitate synchronization of other processes, such as receiving, processing, and/or transmitting signals. In some embodiments, one or more of the devices described herein may form part or all of a MEMS. The described systems may be used, for example, in the following applications: cellular phone, Wi-Fi, satellite radio and GPS receiver, consumer electronics (e.g., printers, digital cameras, gaming consoles, household appliances), automobile (e.g., ride stabilization and roll over detection), space communication and military applications, navigation and wireless systems.
Having thus described several aspects of at least one embodiment of the technology, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the technology. Accordingly, the foregoing description and drawings provide non-limiting examples only.
In addition, while some references have been incorporated herein by reference, it should be appreciated that the present application controls to the extent the incorporated references are contrary to what is described herein.
Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
This application claims priority under 35 U.S.C. §119(e) to U.S. provisional application No. 61/368,216, filed Jul. 27, 2010 under Attorney Docket No. G0766.70022US00 and entitled “Integrated On-Chip GPS and Inertial Navigation System,” the entire contents of which is incorporated herein by reference. This application also claims priority under 35 U.S.C. §119(e) to U.S. provisional application No. 61/368,218, filed Jul. 27, 2010 under Attorney Docket No. G0766.70023US00 and entitled “Integrated On-Chip Microelectromechanical Systems (MEMS) Radio Frequency Components In Transceivers,” the entire contents of which is incorporated herein by reference. This application also claims priority under 35 U.S.C. §119(e) to U.S. provisional application No. 61/368,224, filed Jul. 27, 2010 under Attorney Docket No. G0766.70024US00 and entitled “Monolithically Integrated Piezoelectric Location Awareness Device,” the entire contents of which is incorporated herein by reference. This application also claims priority under 35 U.S.C. §119(e) to U.S. provisional application No. 61/368,227, filed Jul. 27, 2010 under Attorney Docket No. G0766.70025US00 and entitled “Wafer Level Stacking Of MEMS Resonator With IC Wafer,” the entire contents of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61368216 | Jul 2010 | US | |
| 61368218 | Jul 2010 | US | |
| 61368224 | Jul 2010 | US | |
| 61368227 | Jul 2010 | US |
