Abstract:
Sensors for air flow, temperature, pressure, and humidity are integrated onto a single semiconductor die within a miniaturized Venturi chamber to provide a microelectronic semiconductor-based environmental multi-sensor module that includes an air flow meter. One or more such multi-sensor modules can be used as building blocks in dedicated application-specific integrated circuits (ASICs) for use in environmental control appliances that rely on measurements of air flow. Furthermore, the sensor module can be built on top of existing circuitry that can be used to process signals from the sensors. By integrating the Venturi chamber with accompanying environmental sensors, correction factors can be obtained and applied to compensate for temporal humidity fluctuations and spatial temperature variation using the Venturi apparatus.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to the fabrication of microelectronic environmental sensors. 
         [0003]    2. Description of the Related Art 
         [0004]    Mobile computing devices such as smart phones typically include embedded electronic sensors such as, for example, magnetic field sensors (magnetometers) that can be used to determine orientation of the smart phone relative to the earth&#39;s ambient magnetic field. In addition, smart phones typically contain one or more accelerometers that sense the acceleration of gravity directed perpendicular to the earth&#39;s surface, and can detect movement of the smart phone. However, smart phones available today generally do not offer to consumers or program developers features that entail sensing, monitoring, or controlling local environmental conditions. Providing additional environmental sensors within smart phones, tablet computers, and the like, may encourage program developers to create applications that otherwise might not be possible. 
         [0005]    Some existing products contain miniature environmental sensors. For example, electronic climate control devices (e.g., thermostats) rely on electronic sensors to trigger activation of furnaces and air conditioners for feedback control of air temperature and humidity. Electronic weather stations also rely on internal temperature sensors, barometric pressure sensors, and humidity sensors, such as, for example, those described in U.S. patent application Ser. No. 13/310,477 to LeNeel et al. Typically, these miniature environmental sensors are fabricated separately, on separate substrates (dies) from one another, or the sensors are built on one substrate and associated circuitry for signal processing and control is fabricated on a separate die (see, for example, US Patent Application Publication 2012/0171774A1 to Cherian et al.). Separate fabrication processes have been necessary because integrating more than one type of environmental sensor on the same substrate, with circuitry, poses a significant material processing challenge. 
         [0006]    In some applications, chemical sensors have been integrated with circuitry for analyzing a chemical sample (see, for example, US Patent Application Publication 2012/0171713A1 to Cherian et al.). In other applications, chemical sensors can be built into a vehicle for delivering to the micro-sensor a chemical or biological sample for analysis, such as a razor blade (see, for example, US Patent Application Publication 2012/0167392A1 to Cherian et al.) In further applications, it has been possible to integrate temperature and humidity environmental sensors with the chemical sensors, for example, as disclosed in U.S. Patent Application Publications US 2012/0168882 to Cherian et al. However, in general, integration of multiple environmental sensors, including fluid sensors for measuring fluid pressure and flow rates, has been challenging because sensing elements for different environmental conditions typically require different, or even incompatible, materials. It is noted that the references cited above are owned by the applicants of the present patent application, and are hereby incorporated by reference in their entirety. 
       BRIEF SUMMARY 
       [0007]    An air flow meter can be constructed using a Venturi tube in accordance with Bernoulli&#39;s principle. A Venturi tube is a device that directs fluid flow through a constriction, or nozzle. When a fluid, (e.g., a gas or a liquid), is constricted, the fluid velocity increases, and the fluid pressure drops. This fluid behavior can be observed, for example, when water flows through a garden hose nozzle. In an air flow meter, an air flow rate can be calculated from a differential air pressure based on measurements made at an open end and at the nozzle of the Venturi tube. 
         [0008]    Miniaturization of air flow sensors can be accomplished by constructing a Venturi chamber on a semiconductor substrate, and placing microelectronic pressure sensors at the inlet and the outlet of the chamber, that is, on opposite sides of a constriction. Thus, a differential pressure can be measured, and a flow rate can be calculated. Because humidity and temperature variation are known to affect the accuracy of flow measurements using a Venturi tube, it is relevant to include additional sensors for these environmental variables as well. 
         [0009]    The micro-sensor described herein integrates sensors for air flow, temperature, pressure, and humidity onto a single semiconductor die to provide a semiconductor-based environmental sensing module. U.S. patent application Ser. No. 13/853,732 (hereinafter “the &#39;732 patent application”), by the applicant of the present patent application, describes an integrated sensor module that includes temperature, pressure, and humidity sensors. The microelectronic sensing module described herein incorporates the integrated sensor module of the &#39;732 patent application into a sensor package that also includes a micro-fabricated gas flow meter. One or more such sensor packages can be used as building blocks in dedicated application-specific integrated circuits (ASICs) for use in environmental control appliances. Furthermore, the sensing module can be built on top of existing circuitry that can be used to process signals from the sensors. By integrating the Venturi tube and accompanying environmental sensors into a unitary configuration, correction factors can be obtained and applied to compensate for temporal humidity fluctuations and spatial temperature variation using the Venturi apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    In the drawings, identical reference numbers identify similar elements. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. 
           [0011]      FIG. 1A  is a perspective view of a prior art commercial fragrance dispenser showing air flow through the dispenser along three axes. 
           [0012]      FIG. 1B  is a plan view of a prior art air conditioning unit that can be equipped with a Venturi type air flow sensor. 
           [0013]      FIG. 1C  is a perspective view of an arrangement of air flow sensors consistent with embodiments described herein. 
           [0014]      FIG. 2  is a pictorial plan view of a prior art Venturi tube. 
           [0015]      FIG. 3  is a side view of a device profile of a miniaturized Venturi chamber constructed on a semiconductor substrate and equipped with multiple environmental sensors. 
           [0016]      FIG. 4  is a top plan view of the miniaturized Venturi chamber and accompanying environmental sensors shown in  FIG. 3 , including schematics of each of the sensors. 
           [0017]      FIGS. 5-7  show aspects of a finite element numerical simulation of air flow through a Venturi tube model of the miniature Venturi chamber shown in  FIG. 3 . 
           [0018]      FIGS. 8-10B  show aspects of an integrated multi-sensor module as described herein, according to one embodiment. 
           [0019]      FIG. 11A  is a plan view of an ASIC layout of four of the multi-sensor modules shown in  FIG. 10B . 
           [0020]      FIG. 11B  is a plan view of a patterned silicon cap as described herein. 
           [0021]      FIG. 11C  is a plan view of the patterned silicon cap shown in  FIG. 11B , following adhesive bonding to the four multi-sensor modules shown in  FIG. 11A . 
           [0022]      FIG. 12  is a screen shot of a smart phone running a weather station application that displays data from an on-board miniature multi-sensor module that includes an air flow meter. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    It will be appreciated that, although specific embodiments of the present disclosure are described herein for purposes of illustration, various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, the present disclosure is not limited except as by the appended claims. 
         [0024]    In the following description, certain specific details are set forth in order to provide a thorough understanding of various aspects of the disclosed subject matter. However, the disclosed subject matter may be practiced without these specific details. In some instances, well-known structures and methods of semiconductor processing comprising embodiments of the subject matter disclosed herein have not been described in detail to avoid obscuring the descriptions of other aspects of the present disclosure. 
         [0025]    Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and variations thereof, such as “comprises” and “comprising” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” 
         [0026]    Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more aspects of the present disclosure. 
         [0027]    In the following description, certain specific details are set forth in order to provide a thorough understanding of various aspects of the disclosed subject matter. However, the disclosed subject matter may be practiced without these specific details. In some instances, well-known structures and methods of semiconductor processing comprising embodiments of the subject matter disclosed herein have not been described in detail to avoid obscuring the descriptions of other aspects of the present disclosure. 
         [0028]    Reference throughout the specification to insulating materials or semiconducting materials can include various materials other than those used to illustrate specific embodiments of the transistor devices presented. The term “environmental sensors” should not be construed narrowly to mean only sensors for pressure, temperature, and humidity, for example, but rather, the term “environmental sensors” is broadly construed to cover any type of sensor that is capable of monitoring ambient characteristics. 
         [0029]    Reference throughout the specification to conventional thin film deposition techniques for depositing silicon nitride, silicon dioxide, metals, or similar materials include such processes as chemical vapor deposition (CVD), low-pressure chemical vapor deposition (LPCVD), metal organic chemical vapor deposition (MOCVD), plasma-enhanced chemical vapor deposition (PECVD), plasma vapor deposition (PVD), atomic layer deposition (ALD), molecular beam epitaxy (MBE), electroplating, electro-less plating, and the like. Specific embodiments are described herein with reference to examples of such processes. However, the present disclosure and the reference to certain deposition techniques should not be limited to those described. For example, in some circumstances, a description that references CVD may alternatively be done using PVD, or a description that specifies electroplating may alternatively be accomplished using electro-less plating. Furthermore, reference to conventional techniques of thin film formation may include growing a film in-situ. For example, in some embodiments, controlled growth of an oxide to a desired thickness can be achieved by exposing a silicon surface to oxygen gas or to moisture in a heated chamber. 
         [0030]    Reference throughout the specification to conventional photolithography techniques, known in the art of semiconductor fabrication for patterning various thin films, include a spin-expose-develop process sequence involving a photoresist. Such a photolithography sequence entails spinning on the photoresist, exposing areas of the photoresist to ultraviolet light through a patterned mask, and developing away exposed (or alternatively, unexposed) areas of the photoresist, thereby transferring a positive or negative mask pattern to the photoresist. The photoresist mask can then be used to etch the mask pattern into one or more underlying films. Typically, a photoresist mask is effective if the subsequent etch is relatively shallow, because photoresist is likely to be consumed during the etch process. Otherwise, the photoresist can be used to pattern a hard mask, which in turn, can be used to pattern a thicker underlying film. 
         [0031]    Reference throughout the specification to conventional etching techniques known in the art of semiconductor fabrication for selective removal of polysilicon, silicon nitride, silicon dioxide, metals, photoresist, polyimide, or similar materials include such processes as wet chemical etching, reactive ion (plasma) etching (RIE), washing, wet cleaning, pre-cleaning, spray cleaning, chemical-mechanical planarization (CMP) and the like. Specific embodiments are described herein with reference to examples of such processes. However, the present disclosure and the reference to certain deposition techniques should not be limited to those described. In some instances, two such techniques may be interchangeable. For example, stripping photoresist may entail immersing a sample in a wet chemical bath or, alternatively, spraying wet chemicals directly onto the sample. 
         [0032]    Specific embodiments are described herein with reference to examples of integrated micro-sensors that have been produced; however, the present disclosure and the reference to certain materials, dimensions, and the details and ordering of processing steps are exemplary and should not be limited to those shown. 
         [0033]    In the figures, identical reference numbers identify similar features or elements. The sizes and relative positions of the features in the figures are not necessarily drawn to scale. 
         [0034]      FIGS. 1A ,  1 B, and  1 C show different types of three-axis air flow meters used in macroscopic environmental control appliances.  FIG. 1A  shows an example of a fragrance dispenser  100  used in a commercial aromatherapy product. A typical fragrance dispenser  100  may have a diameter  102  of about 0.1 m and a height  104  of about 0.2 m. The fragrance dispenser  100  employs an internal three-axis air flow meter wherein air enters the air flow meter, for example, along axes  106  (left) and  108  (bottom), and leaves the air flow meter along axis  110 .  FIG. 1B  shows an exemplary conventional air conditioning unit  112  having a length  114  of about 1 meter, that also relies on an internal three-axis flow meter.  FIG. 1C  shows a miniaturized combination humidity, pressure, temperature, and flow sensor (HPTF) as described herein. According to one embodiment, the HPTF may be packaged so as to include six environmental micro-sensors having thin film sensing elements: two highly sensitive resistive temperature sensors, two capacitive pressure sensors, one humidity sensor, and one fluid flow sensor in the form of a Venturi chamber. 
         [0035]      FIG. 2  shows a conventional generic Venturi tube  200  that is designed to constrict fluid flow along an axis  202 . The Venturi tube  200  has an inlet  204  of diameter D a  at which fluid enters the Venturi tube  200  at a pressure P a . The Venturi tube  200  further includes a constriction, or nozzle  206 , of diameter D b , in which the fluid pressure increases from P a  to P b . The Venturi tube  200 , as shown, further includes an outlet  208 , of diameter D a  through which the fluid exits. As the fluid passes through the outlet  208 , the pressure decreases back to the value P a  and the flow rate increases accordingly. Two pressure sensors are thus needed to determine a differential pressure Δp which represents the increase in fluid pressure from the inlet  204  to the nozzle  206 , or from the nozzle  206  to the outlet  208 . Applying conservation of energy, the differential pressure, Δp=|P a −P b |, can be calculated from a change in kinetic energy of the fluid as it passes through the nozzle  206 : 
         [0000]        Δp=ρ/ 2( v   f   2   −v   i   2 ),  (1)
 
         [0000]    in which ρ is the fluid density (i.e., fluid mass per unit volume), v i  is the initial fluid velocity, and v f  is the final fluid velocity. Alternatively, a fluid flow rate can be calculated from a differential pressure measurement across the nozzle  206 . 
         [0036]      FIG. 3  shows a side view of a semiconductor-based environmental sensing module  300  built on a substrate  301 , for example, a silicon substrate. The environmental sensing module  300  includes a miniature Venturi chamber  302  that can be constructed as an open cavity between the substrate  301  and an attached, pre-shaped, packaging structure  301   a . In one embodiment, the substrate  301  can be a non-active substrate that is made of crystalline silicon, amorphous silicon (glass), or polysilicon. Alternatively, the miniature Venturi chamber  302  can be constructed on top of active silicon devices. For example, underlying logic circuitry or interconnect circuitry can be configured to read and process sensor signals generated by the miniature Venturi chamber  302 . It is generally advantageous for the substrate  301  to be thermally stable so as to act as a thermal barrier to protect the miniature Venturi chamber  302  and the multi-sensor module from heat generated by surrounding active circuitry. An insulating oxide layer can be deposited on the surface of the substrate  301 , to a thickness of about 2 microns to further separate the miniature Venturi chamber  302  from the substrate  301 . 
         [0037]    The miniature Venturi chamber  302  is designed to constrict gas flow (e.g., air flow) in a transverse direction  303  indicated by arrows pointing from left to right. Although the description herein of the miniature Venturi chamber  302  refers to gas flow, the miniature Venturi chamber  302  can generally serve as a fluid flow meter for a variety of fluids, including both gases and liquids. The miniature Venturi chamber  302  has an upper substrate surface  304  and a lower substrate surface  305 . Two lateral openings in the substrate  301  allow passage of a gas through the miniature Venturi chamber  302  via a gas inlet  306  of a diameter×mm, and a gas outlet  308  of a diameter that is about ten times the diameter of the inlet  306 , or 10×mm. 
         [0038]    Thus, according to the exemplary embodiment shown, the miniature Venturi chamber  302  is constricted at the gas inlet  306 , forming a gas inlet nozzle. However, the miniature Venturi chamber  302  is not so limited. In alternative embodiments, the gas inlet  306  may have, instead, a large diameter relative to a constricted gas outlet  308  (nozzle) of the miniature Venturi chamber  302 . Or, the shape of the miniature Venturi chamber  302  may resemble the generic Venturi tube  200 , in which a nozzle is located between the gas inlet  306  and the gas outlet  308 . 
         [0039]    With reference to the exemplary embodiment shown in  FIG. 3 , gas can enter the miniature Venturi chamber  302  at the gas inlet  306  at a pressure P 2 , flow in the direction  303 , and exit the chamber at the gas outlet  308  at a lower pressure P 1 . Using technology disclosed in the &#39;732 patent application, a first integrated multi-sensor module  309  including a pressure sensor  310  to measure P 2 , a humidity sensor  312 , and a temperature sensor  314  can be mounted on the lower substrate surface  305  for continuous exposure to an ambient environment near the gas inlet  306 . A second multi-sensor module  315  including a temperature sensor  316  and a pressure sensor  318  to measure P 1  can also be mounted on the lower substrate surface  305  for continuous exposure to an ambient environment near the gas outlet  308 . 
         [0040]    Alternatively, the humidity sensor  312  can be located near the gas outlet  308 , or anywhere within the miniature Venturi chamber  302 , because humidity tends to remain constant across the miniature Venturi chamber  302 , whereas pressure and temperature exhibit greater spatial variation. In one embodiment, the humidity sensor  312  can be used as a calibration device, based on the fact that humidity variations cause changes in the density of air, which in turn affects pressure (and therefore flow) measurements (see J. M. Lim et al., “The Humidity Effect on Air Flow Rates in a Critical Flow Venturi Nozzle,” Flow Measurement and Instrumentation, Vol 22 No. 5, October 2011, pp. 402-405). 
         [0041]    A gas (e.g., air) flow rate can be calculated from Δp=|P 2 −P 1 |, and the value of Δp can be adjusted to account for humidity and temperature effects using measured data from the sensors  312 ,  314 , and  316 . Alternatively, the sensors  310 ,  312 ,  314 ,  316 , and  318  can be individual sensors instead of being integrated into the multi-sensor modules  309  and  315 . However, the use of semiconductor-based integrated multi-sensor modules in which the sensors are co-located on a common silicon substrate is advantageous because measurements can be made in substantially the same location. Thus, for example, a temperature correction to the flow rate will tend to be more accurate when the temperature measurements are made at substantially the same location as the corresponding pressure measurements. It is noted that if the gas flow in the direction  303  remains laminar, the temperature sensors  314  and  316  are likely to remain accurate. However, if the gas flow becomes turbulent, the temperature sensors  314  and  316  may not be reliable. 
         [0042]      FIG. 4  shows an exemplary top down view  400  from within the miniature Venturi chamber  302  of the environmental sensing module  300  shown in cross-section in  FIG. 3 . In one embodiment, the lower substrate surface  305  as seen from above, has a substrate width  402  of about 1 cm and a substrate length  404  of about 2 cm. Also shown from a top-down view are the pressure sensor  310 , the humidity sensor  312 , the temperature sensors  314 ,  316 , and the pressure sensor  318 . The temperature sensors  314 ,  316  are desirably made from an active material that has a high thermal coefficient of resistance (TCR) to allow a highly sensitive voltage response to changes in ambient temperature. At the left end of  FIG. 4  is shown a pair of power pads  406 , and an array of output connection pads  408 . The power pads  406  provide a path for supplying common power and ground signals to the various sensors through the integrated multi-sensor modules  309  and  315 . Alternatively, power pads  406  can supply power and ground signals to individual sensors if needed. The output connection pads  408  are configured to receive interconnect circuitry to access sensor output voltages and currents for data collection. 
         [0043]    Below each of the sensors  310 ,  312 ,  314 ,  316 ,  318  is shown an exemplary schematic that embodies the sensor. For example, the pressure sensor  310  can be built according to a first differential capacitor schematic  320 ; the humidity sensor  312  can be built according to a second differential capacitor schematic  322 ; the temperature sensors  314 ,  316 , can be realized as a thin film Wheatstone bridge in accordance with a Wheatstone bridge schematic  324 ; and the pressure sensor  318  can be built according to a third differential capacitor schematic  328 . Each of the sensors is described in further detail in the &#39;732 patent application. 
         [0044]    With reference to  FIG. 2 , the sensors  310 ,  312 ,  314 ,  316 , and  318  allow for correcting calculated values of air flow by modifying equation (1) above to yield Darcy&#39;s equation: 
         [0000]        Δp=P   2   −P   1 =4 fL/dg( v   2 ),  (2)
 
         [0000]    in which L is the length of the Venturi tube, d is the diameter of the Venturi tube, g is the acceleration of gravity, f is a friction factor, and v is the fluid velocity. In particular, the friction factor f varies with the relative humidity of the air. 
         [0045]      FIGS. 5 ,  6 , and  7  describe a finite element simulation of an exemplary Venturi tube model  500  of the miniature Venturi chamber  302  shown in  FIG. 3  (i.e., half of the full Venturi tube  200  shown in  FIG. 2 ).  FIG. 5  shows the geometry of the Venturi tube model  500  as seen from a side view. In the embodiment shown, the constricted diameter, ×, of the Venturi tube model  500  at the inlet  306  is about 0.6 mm and the diameter of the open portion of the Venturi tube model  500  at the outlet  308  is about 10 times 0.6 mm or 6.3 mm. The total length of the tube, L, is 17.6 mm. The length of the constricted region A1 is 7.6 mm; the length of the open portion of the tube A2, at the outlet  308 , is 5.0 mm. A throat region of the tube, A3, is designated between the inlet  306  and the outlet  308 . 
         [0046]      FIG. 6  shows a temporal snapshot  600  taken during a finite element (“nodal”) simulation run in which operation of the miniature Venturi chamber  302  is simulated using the geometry of the Venturi tube model  500 . At the time of the snapshot, air speed at the gas inlet  306  of the Venturi tube model  500  is non-zero, and a pressure difference is therefore evident between the gas inlet  306  and the gas outlet  308 . This pressure difference corresponds to a measurable pressure difference that can be sensed in the miniature Venturi chamber  302  by the pressure sensors  310  and  318 . The snapshot  600  shows a two-dimensional pressure map in which regions of high pressure are indicated by a dark pattern  602 , and regions of low pressure are indicated by an open striped pattern  604 . Thus, the wide open gas outlet  308  is at a low pressure (−0.254E-03), effectively zero mBarr, and the constricted gas inlet  306  is at a maximum pressure of about 20 mBarr, or 0.019 Barr. In the snapshot shown, air moves along an axis  606  of the chamber and has not yet dissipated throughout the low pressure region of the gas outlet  308 , although some diffusion is evident at the far right end  608  of the outlet  308 . 
         [0047]      FIG. 7  shows a curve  700  of the pressure difference Δp in mBarr as a function of the initial air velocity v i  at the inlet  306 , in m/s. According to equation (2) above, the pressure difference varies with the square of the velocity, so the shape of the curve  700  should resemble a parabola. The low-velocity region  702  of the curve  700  corresponds to air flow like that inside a typical room. The medium-velocity region  704  of the curve  700  corresponds to air flow like that outside on a windy day. The high-velocity region  706  of the curve  700  corresponds to air flow like that outside during a wind storm. The change in pressure between the constricted inlet  306  and the open outlet  308  rises from zero mBarr to about 65 mBarr as the air speed at the inlet  306  increases. For example, if the wind speed is zero (still air), there is no discernible pressure drop across the chamber. As the wind speed increases to 80 m/sec, the pressure drop across the Venturi tube increases to about 50 mBarr. 
         [0048]      FIGS. 8-10B  show aspects of the exemplary integrated multi-sensor module  309 , as disclosed in the &#39;732 patent application. 
         [0049]    The module profile  800  can be fabricated on, for example, the lower substrate surface  305  of the substrate  301 . In addition to the pressure sensor  310 , the relative humidity sensor  312 , and the temperature sensor  314 , the module profile  800  further includes a reference pressure sensor  802 . Each environmental sensor includes one or more thin film sensing elements designed to be highly sensitive to environmental conditions. The pressure sensor  310  is designed to be accurate to within about ±1 mBarr; the relative humidity sensor  312  is designed to be accurate to within about ±3%; and the temperature sensor  314  is designed to be accurate to within about ±1 degree. Choice of materials for the various structures shown in  FIG. 3  can determine the degree of success of integrating the various sensors onto a common substrate. 
         [0050]    In the embodiment shown in profile in  FIG. 8 , an active environmental sensor layer  803  is shown constructed on top of an insulating oxide layer  804  that separates the active environmental sensor layer  803  from the substrate  301 . Differential capacitor elements within the active environmental sensor layer  803  include a common bottom plate  806 ; one or more capacitive dielectrics  807 ,  808 ,  809 , and  810 ; and metal mesh top plates  812 ,  814 , and  816 . Resistive temperature sensors such as the temperature sensor  314  include the common bottom plate  806 , the dielectric  807 , a second metal layer  818 , a third metal layer  820 , and a metal cap layer  822 . The common bottom plate  806  may further be used as a heater to calibrate and/or adjust the various sensors according to a calibration protocol as described in the &#39;732 patent application. The pressure and humidity sensors  310  and  312 , respectively, are exposed to the ambient environment through openings  824 . A thick, polyimide protective layer  826  covers the pressure sensor  310  and the reference pressure sensor  802 . 
         [0051]      FIG. 9  summarizes an exemplary sequence of process steps in a method  900  of fabricating the integrated multi-sensor module  309  described below with reference to the module profile  800  shown in  FIG. 8 . At  902 , the insulating oxide layer  804  can be formed on the silicon substrate  301 . The insulating oxide layer  804  can be deposited to a thickness of about 2 microns to further separate the multi-sensor module  309  from the substrate  301 . 
         [0052]    At  904 , a two-layer metal interconnect structure including the second metal layer  818  and the third metal layer  820  can be formed. According to one embodiment, the common bottom plate  806  is shown as being incorporated into each of the capacitive and resistive sensors, but the metal layers  818  and  820  are only shown as being incorporated into the (resistive) temperature sensor  314 . 
         [0053]    At  906 , vias are formed in the dielectric  807  to permit connections between the common bottom plate  806  and the third metal layer  820 . The common bottom plate  806  is desirably made of a refractory metal having a low thermal coefficient of resistance (TCR) such as tantalum aluminum (TaAl), titanium (Ti), or tungsten silicon nitride (WSiN) that can sustain temperatures of several hundred to several thousand degrees Celsius, and that exhibits a medium sheet resistance. 
         [0054]    At  908 , the active sensor layer  803  is formed. Disposed between the metal mesh top plates  812 ,  814 ,  816  and the common bottom plate  806 , for each parallel plate capacitor sensor, is the capacitive dielectric film  808  that is sensitive to ambient environmental conditions. A purpose of the metal mesh top plates  812 ,  814 ,  816  is to provide continuous exposure of the capacitive dielectric films to the same ambient environment through 1-2 μm wide openings  824  in the mesh. When the capacitive dielectric film  808  is exposed to the environment, pressure on the capacitive dielectric film  808  decreases the film thickness, thereby changing the capacitance of the sensor device. Similarly, changes in ambient humidity can cause the capacitive dielectric film  808  to expand or contract, thereby changing the film thickness, and in turn the capacitance of the sensor. 
         [0055]    The desired material for the capacitive dielectric film  808  in the example shown is a 1-4 um thick layer of polyimide for both the humidity sensor  312  and the reference pressure sensor  802 . It is generally advantageous to use a thin capacitive dielectric film  808  (e.g., 1 μm) to reduce topography, thus producing a smoother surface. 
         [0056]    At  910 , cavities are opened in the active sensor layer  803 . The desired material for the capacitive dielectric used in the pressure sensor  310  as shown is air (i.e., the dielectric is formed as a cavity  809  that can be filled by the passage of ambient air through the openings  824  in the mesh top plate  814 ). Between each capacitive dielectric film  808  and metal mesh top plate there can be formed a second dielectric layer  807  of, for example, about 0.5 μm of silicon nitride (Si 3 N 4 ) or silicon carbide (SiC), to provide thermal transmission so as to readily dissipate heat. The metal mesh top plates  812 ,  814 ,  816  can be made of aluminum, or another suitable metal. Surrounding the metal mesh top plates there can be deposited a third dielectric passivation layer  810  of, for example, 0.5 μm-thick silicon nitride (Si 3 N 4 ). In accordance with the embodiment shown, the dielectric/metal/passivation total stack height in the embodiment shown is about 1 μm. The width of the second and third (passivation) dielectrics between the metal mesh top plates and the neighboring openings  824  shown is also about 1 μm. 
         [0057]    The temperature sensor  314  within the integrated multi-sensor module  309  includes exemplary multi-layer resistive elements, one of which is shown in cross section at the far right of  FIG. 8 . Each resistive element can be made up of layers that can include the common bottom plate  806 , a second metal layer  818 , the second dielectric layer  807 , and the third metal layer  820 . The second metal layer  818  can be made of, for example, AlCu. The third metal layer  820  can be made of, for example, aluminum that can be capped with a thin, high TCR metal such as a platinum (Pt) metal cap layer  822  of about 100 Å. Alternatively, the metal cap layer  822  can be made of a chromium silicon (CrSi) material, which also has a high TCR. 
         [0058]    At  914 , after the capacitive sensors  310 ,  312 , and  802  are formed, the thin film sensing elements  808  and  809  can be exposed to ambient conditions by forming openings  824  in the dielectric layers  807  and  810 . 
         [0059]    Next, the thick protective layer  826 , shown in  FIG. 8  as a polyimide film having a thickness of about 6 μm, can be spun on at room temperature to cover portions of the reference pressure sensor  802  and the pressure sensor  310 . An optional silicon nitride (SiN) cap can be deposited to shield the photo-sensitive polyimide protective layer  810  from exposure to light. 
         [0060]    At  914 , the packaging structure  301   a  can be attached to the silicon substrate  301  to form the mini-Venturi chamber  302  around the multi-sensor module  309 . 
         [0061]      FIG. 10A  shows a top-down view of an integrated multi-sensor module  1000  having a configuration similar to the integrated multi-sensor module  800  shown in cross-section in  FIG. 8 , except that the positions of the relative humidity sensor  312  and the pressure sensor  310  have been swapped. 
         [0062]      FIG. 10B  shows the integrated multi-sensor module  900 , over which a patterned passivation layer  902  has been added. In this example, the patterned passivation layer  902  exposes the relative humidity sensor  312  so as to allow the dielectric membrane of the relative humidity sensor  312  ample exposure to ambient moisture variation. The reference pressure sensor  902 , is underneath the patterned passivation layer  902 . The patterned passivation layer  902  also exposes a row of electrical contact pads  904  so that signals are accessible to be read from one or more of the sensors. The patterned passivation layer  902  can be made of a standard passivation material such as polyimide, for example, or silicon nitride. 
         [0063]      FIG. 11A  shows an exemplary ASIC sensor module layout  1100  that includes four passivated multi-sensor modules  900   a - 900   d  (collectively  900 ). Each multi-sensor module  900  is covered by the added passivation layer  902  as shown in  FIG. 9B . The two passivated multi-sensor modules on the left,  900   a  and  900   b , are in a mirror-image configuration, as are the two passivated multi-sensor modules  900   c  and  900   d  on the right. Such a configuration results in greater structural stability after a silicon cap is attached as described below. 
         [0064]      FIG. 11B  shows a patterned silicon cap  1120  for attachment to the ASIC sensor module layout  1100 . The patterned silicon cap  1120  is a silicon wafer, about 300 microns thick, configured with openings  1130 ,  1140 ,  1150  that align with the humidity sensors  312 . The patterned silicon cap  1120  can be adhesively bonded to the layout  1100  to form a laminate that protects portions of each multi-sensor module  900  while allowing contact between the sensor membranes and the ambient environment (e.g., air). The bonding process is desirably carried out at a low temperature. In other embodiments, depending on the application, the openings may align with different sensors, for example, with the humidity sensors  312  so that the reference pressure sensors  802  can be sealed under the silicon cap  1120 . 
         [0065]      FIG. 11C  shows the silicon cap  1120  attached to the ASIC sensor module layout  1100 . The silicon caps  1120  do not cover the temperature sensors  314 , the pressure sensors, the humidity sensors  310 , or the rows of electrical contact pads  904 . Only the reference pressure sensors are covered. Because the openings  1130 ,  1140 , and  1150  are needed for sensing ambient environmental conditions, the final product is essentially environmentally unprotected. However, deployment of a multi-sensor module within a Venturi chamber as described herein provides additional protection so that the silicon cap  1120  itself may be considered an optional element of such an embodiment. 
         [0066]      FIG. 12  shows a smart phone  1200  equipped with a semiconductor-based multi-sensor module  300  that can be used to monitor ambient environmental conditions in real time, including wind speed. A small die size and low power consumption make the multi-sensor module  300  especially suited for mobile computing applications. 
         [0067]    A shell of the smart phone  1200  can be modified so as to allow exposure of the capacitive sensors and the air flow sensor to ambient air flow  1201 . In particular, the smart phone shell can be modified to accommodate the internal air flow meter by including an air entry aperture  1202  in the shell to expose the on-board venturi sensor  1203  to the ambient air flow  1201 . An exemplary smart phone application (“app”) can, for example, be programmed to display on the smart phone screen  1204  weather station icons  1205 . The smart phone app can report measurements of temperature, relative humidity, pressure, and wind speed and direction via the readouts  1206 ,  1207 , and  1208 , and  1209 , respectively. The smart phone app can further provide an assessment of air quality  1210  based on a comparison of the measurements to a selected standard. The standard can be pre-programmed or set by a user of the smart phone, for example. 
         [0068]    The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments 
         [0069]    These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.