Abstract:
A portable apparatus having an accelerometer device and a supporting element in the accelerometer device, having a first body of semiconductor material integrating a sensor element that detects movements of the first body and generates a signal correlated to the detected movement; a second body of semiconductor material that integrates a conditioning electronics and that is electrically connected to the first body; and conductive bumps that provide electrical connection of the first and second bodies to the supporting element. In particular, the conductive bumps connect the first and second bodies to the supporting element without the interposition of any packaging.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a portable apparatus with an accelerometer device for free-fall detection. In particular, the following description will make explicit reference to a portable apparatus provided with a mass storage device (hard disk), without this implying any loss of generality. 
   2. Description of the Related Art 
   As is known, portable electronic devices, such as for example laptops, PDAs (Personal Data Assistants), digital audio players, cell-phones, digital cameras and the like, can readily be subject to violent impact, in particular in the case where they are dropped on the ground during their normal use. In the event of fall, the impact of the portable apparatus on the ground has a particularly detrimental effect on a hard disk within the portable apparatus, in the worst case producing permanent damage and the consequent loss of the stored data. 
   Hard disks are very sensitive to impact in so far as the read/write head is normally kept at a very small distance from the data-storage medium. Consequently, in the event of impact, the read/write head strikes the data-storage medium and can be damaged together with it. 
   In order to prevent, or at least limit, the occurrence of said destructive events, it has been proposed to use linear accelerometers, fixed to the portable apparatus, to detect a free-fall condition of the portable apparatus. Following the free-fall detection, a command is issued for forced parking of the read/write head of the hard disk, which is brought into a safe area of the disk, for example to the position assumed by the head when the apparatus is turned off. 
   The free-fall condition is detected by appropriate processing of the acceleration signals generated by the accelerometer, and in particular by verifying that the acceleration detected along all the measurement axes is zero. 
   Linear accelerometer devices are known, built using semiconductor technology, namely the so-called MEMS (Micro-Electro-Mechanical-Systems). As is known, and illustrated in  FIG. 1 , a linear accelerometer device  1  of a MEMS type includes a sensitive element  2 , which detects the acceleration and generates an electrical signal correlated to the detected acceleration, and a conditioning electronics  3  for the conditioning of the electrical signal, which includes a charge integrator  4  and a gain and noise-cancellation stage  5 , in particular using the CDS (Correlated Double Sampling) technique. 
   It is also known that hard-disk manufacturers are reducing the dimensions of the hard disks, in particular in portable devices, wherein the miniaturization of dimensions is of fundamental importance. However, with current technologies, accelerometer devices have large physical dimensions (in particular as regards thickness), which make their integration within the hard disk an issue. 
   The sensitive element  2  is formed by two distinct portions of semiconductor material (generally silicon): a first portion, in which the microelectromechanical detection structure is formed, and a second portion, which has the function of a protective cap, and is applied to the first portion to seal it hermetically. The microelectromechanical structure must in fact be protected from dust and micrometric corpuscles which could alter its performance and jeopardize its correct operation. The conditioning electronics  3  is bonded on the-surface of the sensitive element  2  whereon contact metallizations are also formed, and electrical connection is obtained using the wire-bonding technique. The conditioning electronics  3  and the sensitive element  2  thus coupled together are coated with a molding resin and enclosed within a package. A structure of the type described cannot have a thickness of less than 1.5 to 2 mm, which prove excessive if compared with the currently required dimensions (a thickness of less than 1.5 mm is required). 
   The accelerometer devices are currently arranged within the portable apparatus in a position outside the hard disk and are generally coupled to the electronic circuit controlling the general operation of the portable apparatus. Such a solution, however, has problems due to the delays in communication of the free-fall detection signals from the accelerometer device to the hard disk. Consequently, the free-fall condition cannot be detected promptly enough to activate the appropriate actions of protection (for example, the parking of the read/write head) and hence prevent damage to the portable apparatus. 
   BRIEF SUMMARY OF THE INVENTION 
   The disclosed embodiments of the present invention provide a portable apparatus that will enable a solution to the aforementioned problems, and in particular will be provided with an accelerometer device having a reduced thickness such as to enable integration of the accelerometer device within the electronic device that it is desired to protect from impact, for example, within a hard disk. 
   In accordance with one embodiment of the invention, a portable apparatus having an accelerometer device and a supporting element is provided, the accelerometer device having a first body of semiconductor material integrating a sensor element configured to detect movements of said first body and generating a signal correlated to said movements; a second body of semiconductor material integrating conditioning electronics, said second body electrically connected to said first body; and electrical connection means for the electrical connection of said first and second bodies to said supporting element, said means of electrical connection connecting said first and second bodies to said supporting element without the interposition of packaging. 
   Ideally, the electrical connection means are in the form of external conductive bumps that are electrically connected between the first and second bodies. 
   In accordance with another aspect of the foregoing embodiment, the first body includes a first die and a cap fixed to said first die for hermetically closing said sensitive element, said cap having first through connections; and wherein said means of electrical connection include first internal conductive bumps electrically connecting said first through connections and said second body, and second internal conductive bumps electrically connecting said second body and said external conductive bumps. 
   In accordance with another aspect of the foregoing embodiment, a surface of the cap facing said supporting element has a first conductive region; and wherein said first internal conductive bumps are in contact with and arranged between said first through connections and said second body, and said second internal conductive bumps in contact with and arranged between said first conductive region and said second body; said external conductive bumps in contact with and arranged between said first conductive region and said supporting element. 
   In accordance with another aspect of the foregoing embodiment, the apparatus further includes an intermediate substrate of semiconductor material provided with second through connections and having a first face facing said first and second bodies and a second face facing said supporting element, said first face having a second conductive region; a first group of said first internal conductive bumps in contact with and arranged between said first through connections and said second conductive region, and a second group of said first internal conductive bumps in contact with and arranged between said second body and said second conductive region; said second internal conductive bumps in contact with and arranged between said second body and said second through connections, and said external conductive bumps in contact with and arranged between said second through connections and said supporting element. 
   In accordance with another embodiment of the invention, a process for manufacturing a portable device is provided that includes forming a first body of semiconductor material integrating a sensor element configured to detect movements of said first body and to generate a signal correlated to said movements; forming a second body of semiconductor material integrating conditioning electronics; electrically connecting said first and second bodies together; and electrically connecting said first and second bodies to a supporting element, comprising connecting said first and second bodies to said supporting element without interposition of packaging. Ideally the electrically connecting the first and second bodies to a supporting element includes connecting external conductive bumps between the first and second bodies and the supporting element. 
   In accordance with another aspect of the foregoing embodiment, forming a first body includes providing a first die, providing a cap having first through connections, and fixing said cap to said first die for hermetically sealing said sensitive element; and wherein electrically connecting said first and second bodies to a supporting element further comprises electrically connecting first internal conductive bumps between said first through connections and said second body, and electrically connecting second internal conductive bumps between said second body and said external conductive bumps. 
   In accordance with another aspect of the foregoing embodiment, the process further includes providing an intermediate substrate of semiconductor material, forming second through connections through said intermediate substrate, and forming a second conductive region on a face of said intermediate substrate; and wherein electrically connecting first internal conductive bumps comprises soldering a first group of said first internal conductive bumps between said first through connections and said second conductive region, and soldering a second group of said first internal conductive bumps between said second body and said second conductive region; and wherein electrically connecting second internal conductive bumps comprises soldering said second internal conductive bumps between said second body and said second through connections, and connecting external conductive bumps comprises soldering said external conductive bumps between said second through connections and said supporting element. 
   In accordance with another embodiment of the invention, an electronic device is provided that includes an accelerometer device and a supporting element, the accelerometer device including a first body of semiconductor material integrating a sensor element, configured to detect movements of said first body and generating a signal correlated to said movements; a second body of semiconductor material integrating a conditioning electronics, said second body being electrically connected to said first body; and electrical connection means for the electrical connection of said first and second bodies to said supporting element without the interposition of a package. 
   In accordance with another embodiment of the invention, an enhanced proximity free-fall detection device without a package for use with a portable hard disk is provided. Ideally the device and the hard disk are micro-encapsulated. The device includes a printed circuit board electrically coupled to the portable hard disk; a free-fall detection module configured to generate a free-fall detection signal upon detection of a free-fall condition to cause the portable hard disk device to attain a protected condition; and an electrical connection system electrically coupling the free-fall detection module to the printed circuit board, the electrical connection system comprising at least one first conductive bump electrically coupling the module to a first body containing a circuit for conditioning the free-fall signal prior to reception by the portable hard disk, and at least one second conductive bump electrically coupling the first body to the printed circuit board. 
   In accordance with another embodiment of the invention, the device includes an intermediate conductive member coupling the first body to the at least one second bump. Ideally, the module includes a through-hole for electrical coupling of a free-fall detection sensor to the at least one first bump, and the at least one first bump physically attaches the module to the printed circuit board without a package. 
   In accordance with another embodiment of the invention, an enhanced proximity free-fall detection device without a package for use with a portable hard disk is provided, preferably in micro-encapsulated form. The device includes a printed circuit board electrically coupled to the portable hard disk; a free-fall detection module configured to generate a free-fall detection signal upon detection of a free-fall condition to cause the portable hard disk device to attain a protected condition; and an electrical connection system electrically coupling the free-fall detection module to the printed circuit board, the electrical connection system including at least one first bump electrically coupling the module to a first intermediate substrate, at least one second bump electrically coupling a first body containing a circuit for conditioning the free-fall detection signal from the module prior to reception by the portable hard disk to the intermediate substrate, and at least one third bump electrically coupling the intermediate substrate to the printed circuit board. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
     For a better understanding of the present invention, there is now described a preferred embodiment thereof purely by way of non-limiting example and with reference to the attached drawings, wherein: 
       FIG. 1  shows a simplified block diagram of a MEMS accelerometer device of a known type; 
       FIG. 2  shows a block diagram of a portable apparatus incorporating an accelerometer device for the detection of a free-fall condition in accordance with the present invention; 
       FIG. 3  shows schematically a side view of an accelerometer device according to a first embodiment of the present invention; and 
       FIG. 4  shows schematically a side view of a second embodiment of the accelerometer device according to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2  is a schematic illustration of a portable apparatus  10  provided with a hard-disk unit (or hard-disk drive unit)  11 , a control electronics  12 , and one or more devices  13 , which are specific for the portable apparatus  10 . The control electronics  12  is connected to the hard-disk unit  11  and to the devices  13 , and is configured to control the general operation of the portable apparatus  10 . 
   The hard-disk unit  11  includes a data-storage medium  14 , a read/write device  15 , and a microprocessor circuit  16 , configured to control operation of the hard-disk unit  11 . The hard-disk unit  11  further includes an accelerometer device  20 , connected to the microprocessor circuit  16  and mounted on a printed-circuit board (PCB)  34 , which also carries the microprocessor circuit  16 . 
   The accelerometer device  20  is of a linear type and has a MEMS device made using semiconductor technology, and has three axes of detection x, y and z, so as to generate three acceleration signals A x , A y , A z , each correlated to the acceleration detected along a respective axis of detection (in a known way which is not described in detail. 
   In particular, according to an aspect of this embodiment of the invention, the accelerometer device  20  is without a package, so as to have a reduced thickness, thus compatible with the physical dimensions of the hard-disk unit  11 , and so as to allow integration within the hard-disk unit  11 . 
   In detail, and as illustrated schematically in  FIG. 3 , the accelerometer device  20  includes a sensor element  22 , which generates an electrical signal as a function of the detected acceleration (typically a capacitive unbalancing signal), and a conditioning electronics  23 , which receives the electrical signal and processes it appropriately (typically via operations of amplification and filtering; see also  FIG. 1 ). 
   The sensor element  22  is integrated within a body of semiconductor material (generally silicon) formed by two portions, namely a first die  25  and a cap  26 . The sensor element  22  is made using MEMS techniques and constitutes the sensitive part of the accelerometer device  20 , generally comprising a fixed stator and a rotor, which is mobile with respect to the stator as a function of the detected acceleration, both the stator and the rotor being of a known type and so not illustrated in  FIG. 3 . For example, the sensor element  22  can be made as described in “3-axis digital output accelerometer for future automotive applications”, B. Vigna et al., AMAA 2004. 
   The cap  26  hermetically closes the first die  25  and is attached to the latter via any bonding technique of a known type, for example via “glass-frit bonding” or “anodic bonding”. The surface of the cap  26  not connected to the first die  25  carries first metallizations  27 , and the cap  26  is equipped with first through connections  28 , insulated from one another. The first through connections  28  can be made using any known technique, for example by means of metallized through holes (vias), or by means of the technique described in EP-A-1151962 and EP-A-1351288. 
   The conditioning electronics  23  is provided in a second die  29  of semiconductor material (typically silicon), which is distinct with respect to the sensor element  22 . 
   The electrical connection between the sensor element  22  and the second die  29  is obtained using the “flip-chip” technique by means of first conductive bumps  30 , set in electrical contact with, and arranged between, the first through connections  28  and electrical contacts provided on the surface of the second die  29 . Second conductive bumps  31  connect together and are arranged between further electrical contacts provided on the surface of the second die  29  and the first metallizations  27 . The first metallizations  27  are in turn connected to the printed-circuit board  34  via third conductive bumps  32 . The third conductive bumps  32  have a diameter greater than the first and second conductive bumps  30  and  31 , and are made using BGA (Ball Grid Array) techniques. In particular, the third conductive bumps  32  connect together and are arranged between the first metallizations  27  and corresponding electrical contacts formed on the surface of the printed-circuit board  34 . 
   Illustrated with a dashed and dotted line in  FIG. 3  is a possible path of the electrical signals transferred from the sensitive element  22  to the conditioning electronics  23 , through the first through connections  28  and the first conductive bumps  30 , and from the conditioning electronics  23  to the printed-circuit board  34 , through the second conductive bumps  31 , the first metallizations  27  and the third conductive bumps  32 . 
   In detail, the diameter of the third conductive bumps is greater than the sum of the thickness of the second die  29  and the diameter of the first conductive bumps  30 , so that the second die  29  remains arranged between the cap  26  and the printed-circuit board  34 . The diameter of the third conductive bumps  32  is preferably greater than the sum indicated above so as to enable compensation of the thermal stresses caused by the different coefficient of thermal expansion of the semiconductor material of the cap  26  and of the material constituting the printed-circuit board  34  (generally vitreous or plastic material). The first and the second conductive bumps  30 ,  31  may, instead, be of a smaller size in so far as they electrically connect two materials having approximately the same coefficient of thermal expansion. 
   It should be noted that, for reasons of convenience of illustration, just one first through connection  28 , just one first conductive bump  30  and second conductive bump  31 , and just one first metallization  27  are shown in  FIG. 3 . Furthermore, only some of the conductive bumps illustrated carry electrical signals, whilst others have only structural functions of connection. It will in any case appear obvious to a person skilled in the art that the number of first through connections  28 , of first, second and third conductive bumps  30 ,  31 ,  32 , and of first metallizations  27 , as well as their arrangement, can vary according to the number and the type of signals that are to be exchanged between the sensor element  22 , the conditioning electronics  23 , and the printed-circuit board  34 . 
   A second embodiment of the accelerometer device  20  is illustrated in  FIG. 4 , in which parts that are similar are identified with the same reference numbers used in  FIG. 3  and are not described again. 
   In this second embodiment, both the second die  29  and the sensor element  22  are connected to an intermediate substrate  40  of semiconductor material (generally silicon). In detail, the intermediate substrate  40  has a first face facing the second die  29  and the sensor element  22 , and a second face  40   b  facing the printed-circuit board  34 . Second metallizations  41  are formed on the first face  40   a,  and second through connections  47 , which are insulated from one another, are formed through the intermediate substrate  40 . 
   In this second embodiment, a first group of first conductive bumps  30 , designated by the reference number  30   a , connects together and is arranged between the first through connections  28  made through the cap  26  and the second metallizations  41 , whilst a second group of first conductive bumps  30 , designated by the reference number  30   b,  connects together and is arranged between the second die  29  and the second metallizations  41 . The second conductive bumps  31  connect together and are arranged between the second die  29  and the second through connections  47 . Finally, the third conductive bumps  32  connect together and are arranged between the second through connections  47 , on the opposite side with respect to the second conductive bumps  31 , and the printed-circuit board  34 . The diameter of the third conductive bumps  32  is once again greater than that of the first and second conductive bumps  30 ,  31  for reasons of compensation of the thermal stresses. 
   Also in  FIG. 4 , a possible path of the electrical signals exchanged between the sensitive element  22  and the conditioning electronics  23 , and from this to the printed-circuit board  34 , is indicated with a dashed and dotted line. 
   Furthermore, once again the number of first and second through connections  28 ,  47 , of first, second and third conductive bumps  30 ,  31 ,  32  and of second metallizations  41 , as well as their arrangement, can vary with respect to what is illustrated in  FIG. 4 , according to the number and the type of signals that must be exchanged between the sensitive element  22 , the conditioning electronics  23 , and the printed-circuit board  34 . 
   Even though this second embodiment provides a thickness greater than the first embodiment illustrated in  FIG. 3 , it has the advantage of having a greater simplicity of implementation. Also in this second embodiment, the accelerometer device  20  is not provided with a package so that it has small dimensions (in particular as regards thickness), and can thus be integrated within the hard-disk unit  11 . 
   In particular, both the embodiments described enable a thickness of the accelerometer device  20  of less than 0.7 mm to be obtained, and hence it is approximately half the thickness of accelerometer devices of a traditional type. 
   The advantages of the described portable apparatus are clear from the foregoing description. 
   It is in any case emphasized that the reduced thickness of the accelerometer device, and its consequent integration within the hard disk, enables a greater rapidity of response to be obtained following upon the determination of free fall, so as to prevent damage to the portable apparatus and in particular to the hard disk. 
   Furthermore, calibration operations of the sensitive element and of the conditioning electronics of the accelerometer device are facilitated. In fact, the calibration is normally carried out when the conditioning electronics and the sensitive element are encapsulated within a package, such a package using a molding resin, which renders said operation problematical. In this case, instead, the aforesaid parts of the accelerometer device are directly accessible, and it is thus possible to correct any operating faults more easily. 
   Finally, the absence of molding resin around the sensitive element sensibly reduces the thermomechanical stresses and the consequent thermal drifts of the electrical signals generated by the accelerometer device. 
   Finally, it is clear that modifications and variations can be made to the portable apparatus described herein, without thereby departing from the scope of the present invention, as defined in the annexed claims. 
   In particular, the detection of the free-fall condition may not be entrusted to the microprocessor of the hard-disk unit, but to the conditioning electronics of the accelerometer device. A solution of this sort enables even faster intervention times. 
   Other techniques of electrical connection can be used for the electrical connection between the sensitive element and the conditioning electronics, different from the ones illustrated and described. In particular, it is emphasized once again that the number of through connections, conductive bumps, and metallizations may vary according to the number and type of signals exchanged between the accelerometer device and the circuit of the hard disk. 
   Finally, even though the entire description regards the free-fall detection for the protection of a hard disk, it is clear that the accelerometer device can be used for other functions, for example for detecting a displacement imparted upon the portable apparatus for exiting from a condition of stand-by. In addition, the free-fall detection could be used for activating further actions of protection not linked to the protection of the hard disk but of other parts of the portable apparatus. 
   All of the above 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. 
   From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims and the equivalents thereof.