FIELD OF INVENTION

This invention relates to electronic resonators and in particular to integrating a resonating element with a semiconductor temperature sensing element such as a silicon diode to form a resonator with an integrated and closely thermally coupled temperature sensor.

BACKGROUND OF THE INVENTION

Resonators such as, for example, quartz crystal resonators, are used in a number of applications as an alternative to temperature compensated oscillators. In such applications, compensation for frequency changes due to changing ambient temperature is done computationally by the application system software. Such computational temperature compensation necessitates the ability to accurately sense the resonator's temperature. Early implementations involved installing temperature sensing components such as thermistors on the system PCB in close vicinity of the resonator. However, the temperature differential between the resonator and the temperature sensing component results in significant computational temperature compensation errors, the latter increasing at higher rates of ambient temperature change. Various packaging solutions have been deployed aiming at bringing the resonator and the temperature sensing component closer in spatial and thermal sense. These solutions usually utilise an aluminium oxide ceramic package housing both the resonator and the temperature sensing component.

Semiconductor diodes can be used as temperature sensing components as an alternative to thermistors. For such devices, the present invention offers an alternative to using a ceramic package to house a resonator and a diode: in the present invention the unpackaged diode die itself becomes part of the package carrying and encompassing the resonator. Such a structure offers a closer thermal connection between the resonator and the diode, thus significantly reducing the temperature differential between the two elements.

It is therefore an object of this invention to provide an alternative form of resonator closely thermally coupled to and integrated with a semiconductor temperature sensor, or to at least provide the public with a useful choice.

SUMMARY OF THE INVENTION

In a first aspect the invention may broadly be said to consist of an integrated resonator plus diode device comprising:

a semiconductor substrate with two main surfaces and at least one diode, or a circuit functionally equivalent to a diode, formed on one of the said two main surfaces of the said substrate, a resonating element closely associated with, and mounted on one of the said two main surfaces of the said substrate,

a multiplicity of electrically conductive elements formed on one of the said two main surfaces of the said substrate,

and wherein the diode circuitry and the resonating element are electrically connected to at least some of the said electrically conductive elements and wherein at least some of the electrical connections are formed through electrically conductive vias traversing through the substrate.

Preferably the said multiplicity of electrically conductive elements are formed on the surface of the substrate opposing the surface on which the resonating element is mounted.

Preferably the substrate is a silicon substrate and each substrate via is a through silicon via (TSV).

Preferably the resonating element is a quartz crystal resonating element. Alternatively, the resonating element can be of another known type, for example a MEMS resonator, a Bulk Acoustic Wave resonating element, an AT-cut crystal resonating element, an SC-cut crystal resonating element, a High Frequency Fundamental crystal resonating element, a surface Acoustic Wave resonating element, or a Tuning Fork crystal resonating element.

Preferably the said circuit functionally equivalent to a diode is comprised of a suitably configured transistor network intended for temperature sensing.

Preferably, the resonating element is housed in a hermetically sealed space formed by mounting a cap onto the surface of the substrate that the resonating element is mounted on. Alternatively, the substrate with the mounted resonating element can be installed in a single-cavity enclosing ceramic package, with the cavity hermetically sealed by a lid.

Preferably, the diode circuitry is formed on the same substrate surface that the resonator element is mounted on. Alternatively, the diode circuitry can be formed on the opposing surface of the substrate - in this case the number of TSVs required for electrical connections to the external conductive elements is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described by way of example only and with reference to the drawings, in which :

Figure 1 shows a first embodiment of the invention.

Figure 2 shows a second embodiment of the invention.

Figure 3 shows a third embodiment of the invention.

Figure 4 shows a fourth embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A first embodiment of the invention is shown in Figure 1.

A diode (or a semiconductor circuit functionally equivalent to a diode) (1) is formed in the upper surface of a silicon substrate (2). Resonating element mounting pads (3) are formed on the same substrate surface and a resonating element (4) is mounted onto the substrate (2) utilising conductive glue (6) to electrically connect the mounting pads (3) and the resonating element (4). A silicon cap (5) attached to the substrate (2) is used to form, in conjunction with the substrate (2), a hermetically sealed enclosure for the resonating element (4). User access pads (8) are formed on the other (lower) surface of the substrate (2) and through silicon vias (7) are used to electrically connect the resonating element (4) and the diode (1) to the user access pads (8).

A second preferred embodiment of the invention is shown in Figure 2.

This embodiment comprises essentially the same constituent components as the embodiment shown in Figure 1. The main difference with the second embodiment is that the diode (or the semiconductor circuit functionally equivalent to a diode) (1) is formed on the surface of the silicon substrate (2) that is opposed to the surface onto which the resonating element (4) is mounted. The advantage of the second embodiment compared to the first one is that it does not require TSVs to connect the diode circuit (1) to the user access pads (8), thus reducing the number of TSVs (7) required to be made. The trade off, however, is in a reduced thermal coupling between the resonating element (4) and the temperature sensing diode (1) compared to that in the first preferred embodiment of Figure 1.

A third preferred embodiment of the invention is shown in Figure 3.

In this embodiment, instead of using a silicon cap (element 5 in Figure 1) to create a hermetically sealed environment for the resonating element (4), the substrate (2) with the mounted resonating element (4) as in Figure 1 are placed in a cavity of a ceramic package (14) and a lid (15) is utilized to hermetically seal the said cavity. To maintain the electrical connections required, conductive pads (9) formed on the lower surface of substrate (2), conductive pads (10) formed on the inner surface of the ceramic package (14) and conductive balls (12) are utilised in a way well known in the art. This embodiment maintains the close thermal coupling between the resonating element (4) and the temperature sensing diode (1) which is characteristic of the first preferred embodiment, but it lends itself better to a singularised units process flow rather than a wafer processing flow preferable for producing devices of the first embodiment.

A fourth preferred embodiment of the invention is shown in Figure 4.

In this embodiment, instead of using a silicon cap (element 5 in Figure 2) to create a hermetically sealed environment for the resonating element (4), the substrate (2) with the mounted resonating element (4) as in Figure 2 are placed in a cavity of a ceramic package (14) and a lid (15) is utilized to hermetically seal the said cavity. To maintain the electrical connections required, conductive pads (9) formed on the lower surface of substrate (2), conductive pads (10) formed on the inner surface of the ceramic package (14) and conductive balls (12) are utilised in a way well known in the art. This embodiment maintains the close thermal coupling between the resonating element (4) and the temperature sensing diode (1) which is characteristic of the second preferred embodiment, but it lends itself better to a singularised units process flow rather than a wafer processing flow preferable for producing devices of the second embodiment.