Power microelectronic device

Abstract

Title: Microelectronic Power Device The invention relates to a power device comprising: - High electron mobility transistors (T1, T2, T3) formed on an active layer (11), each transistor (T1, T2, T3) comprising a source finger (S), a drain finger (D), and a gate finger (G), - A source contact (S') common to the source fingers (S), - A drain contact (D') common to the drain fingers (D), - A gate contact (G') common to the gate fingers (G). Advantageously, at least one gate finger is not connected to the gate contact (G') and forms a Schottky contact (CS) with the active layer (11). This gate finger (CS) advantageously forms, with the adjacent drain finger (D), a Schottky diode (DS) configured to measure an operating temperature within the power device. Figure for the abstract: Fig. 2A

Description

Title of the invention: Power microelectronic device technical field

[0001] The present invention relates to the field of microelectronics. It finds a particularly advantageous application in the measurement of temperature for power components, typically for GaN-based HEMT (acronym for "High Electron Mobility Transistor") type transistors. STATE OF THE ART

[0002] Power components are designed to operate with high current densities and / or high operating voltages. The operation of these components generates significant heat, with operating temperatures that can reach 150°C. One challenge related to the design of these power components concerns the efficiency of heat dissipation. Another challenge concerns the control of the operating temperature of these components.

[0003] To address these challenges, it is necessary to know the temperature of these components during operation. Several methods have been developed to measure or estimate the temperature of these components. One direct measurement method consists of placing a temperature sensor, for example, a metal coil, near the component to be characterized. By injecting a constant current into the coil and measuring the voltage across its terminals, a direct temperature measurement is obtained. For HEMT transistors, the metal coil can be replaced by a conductive bar placed above the two-dimensional (2DEG) electron gas circulating in the HEMTs. The paper "Linear Temperature Sensors in High-Voltage GaN-HEMT Power Devices, R. Reiner et al., 2016 IEEE Applied Power Electronics Conference and Exposition (APEC)" discloses such a temperature sensor integrated within a HEMT transistor architecture.This solution, however, increases the size of the HEMT transistor-based device. Furthermore, the temperature sensor's conductive bars are positioned between two HEMT transistors. Therefore, the temperature is measured next to the transistors. This sensor does not accurately measure the actual operating temperature within the transistor.

[0004] For other types of components, particularly for MOS transistors (acronym for "Metal Oxide Semiconductor"), it is possible to take advantage of the structure of these MOS transistors to measure a diode characteristic structurally present within the MOS transistors. This diode, called the "diode body," is typically formed by a PN junction between the transistor's cells. A voltage measurement across this diode body provides indirect access at the transistor's operating temperature. The temperature is measured within the transistor itself. This method, which relies on a specific component structure, is not applicable to all components. HEMT transistors, in particular, cannot be characterized using this method.

[0005] An object of the present invention is to propose a temperature sensor architecture for a power component overcoming the disadvantages mentioned above.

[0006] In particular, an object of the present invention is to provide a power microelectronic device comprising HEMT transistors and a temperature sensor with a reduced footprint.

[0007] Another object of the present invention is to provide a power microelectronic device comprising HEMT transistors and a temperature sensor exhibiting improved measurement accuracy.

[0008] The other objects, features and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY

[0009] To achieve this objective, according to one embodiment, a power microelectronic device is provided comprising: - A plurality of elementary high-electron-mobility transistors formed on an active layer and connected in parallel, each elementary transistor comprising a source finger, a drain finger, and a gate finger interposed between the source finger and the drain finger, - A common source contact for the source fingers, - A common drain contact for the drain fingers, - A grid contact common to the grid fingers.

[0010] Advantageously, at least one gate finger is not connected to the gate contact and forms a Schottky contact with the active layer. Advantageously, said at least one gate finger forms with the adjacent drain finger at least one Schottky diode configured to measure an operating temperature within the power microelectronic device.

[0011] The microelectronic device thus features a temperature sensor integrated within a plurality of elementary transistors, in the form of a Schottky diode. This sensor utilizes at least one gate finger and one drain finger of an elementary transistor, which are existing components of the power microelectronic device. The integration of the sensor within the power microelectronic device is complete. The sensor's footprint within the power microelectronic device is very small, even negligible.

[0012] Furthermore, by utilizing the existing design of a basic transistor, the Schottky diode exhibits voltage-withstanding characteristics equal to those of the basic transistor from which it is formed. The temperature measured by the Schottky diode is very close to, or even equal to, the actual operating temperature of a basic transistor in the power microelectronic device. The measurement accuracy of the sensor with respect to the actual operating temperature of the basic transistors is improved.

[0013] One principle of the invention is to locally measure an operating temperature using a Schottky diode by replacing an existing gate finger of a power microelectronic device with a Schottky contact. According to one embodiment, several gate fingers can be replaced by Schottky contacts, so as to form several Schottky diodes within the power microelectronic device. It is thus possible to obtain several localized temperature measurements. An operating temperature map of the power microelectronic device can advantageously be performed by the sensor according to the invention. This makes it possible to detect potential hot spots during the operation of the power microelectronic device. This makes it possible to prevent or avoid failures of the power microelectronic device. BRIEF DESCRIPTION OF THE FIGURES

[0014] The aims, objects, features and advantages of the invention will become clearer from the detailed description of embodiments thereof, which are illustrated by the following accompanying drawings in which:

[0015] [Fig.1A] [Fig.1B] Figures IA, IB schematically illustrate, respectively in top view and in cross-section, a power microelectronic device comprising HEMT transistors, according to the prior art.

[0016] [Fig.2A] [Fig.2B] Figures 2A, 2B schematically illustrate, respectively in top view and in cross-section, a power microelectronic device comprising HEMT transistors and a temperature sensor, according to an embodiment of the present invention.

[0017] [Fig.3] Fig.3 schematically illustrates, in top view, a matrix of HEMT transistors of a power microelectronic device, within which temperature sensors are distributed according to an embodiment of the present invention.

[0018] [Fig.4A] Fig.4A schematically illustrates a temperature sensor in the form of a Schottky diode integrated into the HEMT transistors of a power microelectronic device, according to an embodiment of the present invention.

[0019] [Fig.4B] Fig.4B schematically illustrates a temperature sensor in the form of a Schottky diode integrated into the HEMT transistors of a power microelectronic device, according to another embodiment of the present invention.

[0020] [Fig.5] Fig.3 schematically illustrates, in top view, a power microelectronic device comprising a HEMT transistor matrix and an integrated temperature sensor, according to an embodiment of the present invention.

[0021] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of the principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, in the schematic diagrams, the thicknesses of the different layers and the dimensions of the different elements (fingers, contacts, etc.) are not representative of reality. DETAILED DESCRIPTION

[0022] Before proceeding with a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are listed below:

[0023] According to one example, at least one gate finger forming the Schottky contact is connected to the adjacent source finger. This allows only one Schottky diode to be maintained between said gate finger and the adjacent drain finger. This avoids the need to form another diode between said gate finger and the adjacent source finger.

[0024] According to one example, this neighboring source finger is connected to the source contact of the power microelectronic device, so that the operating temperature is measured via said source contact. The measurement is typically taken in the cutoff state of the elementary transistors, in the third quadrant of the characteristic curve of these elementary transistors.

[0025] According to another example, the microelectronic power device comprises at least one sensing contact independent of the source, drain, and gate contacts, and the adjacent source finger, i.e., the source finger connected to the at least one gate finger forming the Schottky contact, is connected to said at least one sensing contact, so that the operating temperature is measured via said at least one sensing contact. The measurement is performed independently of the operation of the elementary transistors.

[0026] In one example, the device further comprises a barrier layer, for example based on AlGaN, interposed between the active layer and the grid fingers. In one example, at least one grid finger forming the Schottky contact passes at least partially through said barrier layer. In an alternative example, at least one grid finger forming the Schottky contact is disposed on said barrier layer. The contact Schottky can be achieved by etching the AlGaN-based barrier layer, then etching a few nanometers of the GaN-based active layer, and finally depositing a metal, for example, at least 60 nanometers of TiN or a few hundred nanometers of Nickel. This allows for lateral contact with the second-order grid (2DEG). The metals are chosen based on their work function to tailor the Schottky barrier as needed.

[0027] According to one example, the at least one gate finger forming the Schottky contact comprises a plurality of gate fingers which, together with their respective neighboring drain fingers, form a plurality of Schottky diodes, each configured to measure an operating temperature within the power microelectronic device. This allows temperatures to be measured in different areas of the device. If the anodes of the Schottky diodes are all connected to the source contact, an average temperature measurement is obtained. If the anodes of the Schottky diodes are connected to independent contacts, local temperature measurements are obtained.

[0028] According to one example, the power microelectronic device comprises a plurality of independent sensing contacts, and the gate fingers of the plurality of Schottky diodes are connected to said independent sensing contacts, so that the operating temperatures are measured via said sensing contacts. This allows local temperature measurements to be made, for example, over several areas of the device.

[0029] By way of example, a single sensing contact from the plurality of independent sensing contacts corresponds to a single gate finger from the plurality of Schottky diodes. This allows for local and spot temperature measurements. Temperature mapping within the device can advantageously be performed.

[0030] In one example, the elementary transistors are arranged in a matrix. In another example, the Schottky diodes are randomly distributed within said matrix. In yet another example, the Schottky diodes are distributed symmetrically within said matrix. The Schottky diodes can be distributed according to the device's hot spots, for example, to prevent device failure or to monitor heat dissipation within the device.

[0031] According to one example, the elementary transistors are arranged in a rectangular matrix, and the device comprises at least four Schottky diodes positioned at the four corners of said rectangular matrix. The temperature measured at the corners of the device may be partly due to adjacent devices.

[0032] Unless otherwise required, it is understood that all the above optional features and / or variants indicated may be combined to form an embodiment that is not necessarily illustrated or described. Such an embodiment is obviously not excluded from the invention.

[0033] Within the framework of the present invention, the envisaged power device architectures are based on a principle of two-dimensional electron gas conduction (2DEG).

[0034] High Electron Mobility Transistor (HEMT) transistors are based, in particular, on this two-dimensional electron gas architecture. For reasons of power handling (especially at high voltage) and temperature resistance, the semiconductor material of these transistors is preferably chosen to exhibit a wide band gap. Among HEMT transistors with a wide band gap, gallium nitride-based transistors are generally preferred.

[0035] It is specified that, within the framework of the present invention, the terms "on", "overcomes", "covers", "underlying", "opposite" and their equivalents do not necessarily mean "in contact with". Thus, for example, the deposition of a first layer on a second layer does not necessarily mean that the two layers are directly in contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it, or by being separated from it by at least one other layer or at least one other element.

[0036] For example, and in a way known per se in the field of GaN-based HEMT transistors, a thin AIN layer can be intercalated between two GaN and AlGaN semiconductor layers.

[0037] A layer may also be composed of several sub-layers of the same material or of different materials.

[0038] A substrate, stack, layer, "based" on a material A means a substrate, stack, layer comprising only that material A or that material A and possibly other materials, for example alloying elements and / or dopant elements.

[0039] The doping ranges associated with the different types of doping possibly indicated in this application are as follows: - P++ or n+-l- doping: greater than 1 x 102°cm3 - p+ or n+ doping: 1 x 10¹⁸ cm³ to 9 x 10¹⁹ cm³ - Doping p or n: 1 x 1017 cm3 to 1 x 1018 cm3 ic 'yi “7 'y - Intrinsic doping or unintentional doping: 1.10 cm to 1.10 cm

[0040] A preferably orthonormal coordinate system, comprising the x, y, z axes, is shown in the attached figures.

[0041] In the present patent application, the height of an element, typically a grate or drain finger, is taken along the z-axis. The thickness of a layer is taken along a direction normal to the principal extension plane of that layer. Thus, a layer can typically have a thickness along the z-axis. The relative terms "on," "above," "under," "sub-," "upper," and "lower" refer to positions taken along the z-axis.

[0042] The terms "vertical" and "vertically" refer to a direction along z. The terms "lateral" and "laterally" refer to a direction in the xy plane.

[0043] An element located "in line with" or "directly above" another element means that these two elements are both located on the same line perpendicular to a plane in which extends mainly a lower or upper face of a substrate, that is to say on the same line oriented vertically in the figures.

[0044] The terms "approximately", "about", "on the order of" mean "to within 10%" or, when referring to an angular orientation, "to within 10°" and preferably "to within 5°". Thus, a direction substantially normal to a plane means a direction having an angle of 90+10° with respect to the plane.

[0045] Figures IA and IB illustrate, respectively, in top view and cross-section, a power device comprising several elementary HEMT transistors T1, T2, T3. This arrangement is known. It alternates, in the conventional manner, along the x-direction, a drain finger D, a gate finger G, a source finger S, a gate finger G, a drain finger D, a gate finger G, and a source finger S.

[0046] The drain fingers D are connected via a connector 31 to a drain contact D'. The connector 31 conventionally comprises vias and metal tracks.

[0047] The grid fingers G are connected via a connector 32 to a grid contact G'. The connector 32 also conventionally includes vias and metal tracks.

[0048] The source fingers S are connected via a connector 33 to a source contact S'. The connector 33 also conventionally includes vias and metal tracks.

[0049] The elementary HEMT transistors T1, T2, T3 are typically formed on a substrate comprising a support layer 10, for example silicon-based, and an active layer 11 based on GaN. This active layer 11 may, in a known manner, comprise various sublayers based on GaN and / or AlGaN, for example Buffer and / or nucleation layers. A barrier layer 12, typically based on AlGaN, allows the formation of a two-dimensional electron gas (2DEG) in the active layer 11. This 2DEG gas allows current to flow between the drain finger D and the source finger S of an elementary transistor. The current flow is controlled by a voltage Vgs applied between the gate finger G and the source finger S. When this voltage is greater than the threshold voltage Vth of the transistor, the transistor is conducting. The on-state voltage characteristic (first quadrant) of the HEMT transistor typically exhibits a linear regime and a saturation regime. When the voltage Vgs is less than the threshold voltage Vth of the transistor, the transistor is blocking. The off-state voltage characteristic (third quadrant) of the HEMT transistor is not solely temperature-dependent.This characteristic is also impacted by the gate bias (Vgs). Therefore, it is not possible to accurately determine the temperature of the HEMT transistor from the third quadrant characteristic.

[0050] To overcome this drawback, a structural modification of the device is carried out.

[0051] As illustrated in Figures 2A and 2B, a gate finger of an elementary HEMT transistor is modified to obtain a Schottky contact CS which, together with the adjacent drain finger D, forms a Schottky diode DS. This modification consists, in particular, of disconnecting the gate finger 34 from the gate contact G'. The Schottky diode DS is then formed. The disconnected gate finger CS corresponds to the anode of the Schottky diode DS. The drain finger D corresponds to the cathode of the Schottky diode DS. This Schottky diode DS advantageously forms a temperature sensor for the device. The forward characteristic of the Schottky diode DS is indeed temperature-dependent. The temperature affects the slope of the diode's characteristic curve as well as its Vf value (Schottky threshold voltage). To measure the temperature, a constant current is first injected from the anode to the cathode (forward direction) into this Schottky diode DS.The potential difference is then measured across the terminals of the DS Schottky diode. Using a calibration table, for example from the curves presented in the document "UHF IGZO Schottky diode, A. Chasin et al., International Electronic Device Meeting - IEDM 2012", the temperature at the DS diode can be determined from the measured potential difference. For example, for an injected current of 0.1 A / mm and a measured voltage drop of 0.25 V, a temperature of 378 K, or 105 °C, is determined.

[0052] A determination of the local temperature of the device is therefore possible from the forward I(V) characteristic, in the third quadrant, of the DS Schottky diode. The temperature sensor formed by the DS Schottky diode is advantageously fully integrated into the power microelectronic device.

[0053] Preferably, the disconnected grid finger CS and the source finger S are connected by a connector 35. This avoids forming a second diode in the opposite direction between the disconnected grid finger CS and the source finger S.

[0054] As illustrated in Figures 2A and 2B, the disconnected gate finger CS can be structurally identical to the other gate fingers G. This minimizes structural modifications to the device. The manufacturing cost of the temperature sensor within the power microelectronic device is reduced. According to another possibility not shown, the disconnected gate finger CS can extend along z, at least partially, within the barrier layer 12. This allows for adjusting the threshold voltage and the characteristic of the Schottky diode DS.

[0055] As illustrated in [Fig. 3], the power microelectronic device typically comprises several dozen elementary HEMT transistors arranged in an L1, L2, L3 matrix. The drain contact D' is common to all drain fingers D. The source contact S' is common to all source fingers S. The gate contact G' is common to all gate fingers G. It is advantageously possible to locally modify some gate fingers to form Schottky contacts CS. This provides several temperature sensors distributed within the L1, L2, L3 matrix of elementary HEMT transistors.

[0056] Figure 3 illustrates two Schottky CS contacts fully integrated into the device. Different distributions of Schottky CS contacts within the L1, L2, L3 matrix can be considered. In one possibility, four Schottky CS contacts can be formed at the four corners of the L1, L2, L3 matrix. In another possibility, Schottky CS contacts can be placed at the hot spots of the device. This allows monitoring of the device's operating temperature and prevents potential device failure.

[0057] When the location of the sensors within the L1, L2, L3 matrix is ​​chosen, different measurement configurations are possible. Figures 4A and 4B illustrate some of these configurations.

[0058] According to a possibility illustrated in [Fig. 4A], the anodes of the DS diodes are connected to the source contact S', for example via connector 35 with the source finger adjacent to the Schottky contact CS. In this case, the temperature measurement is an average measurement over all the sensors of the device. The measurement is performed here with the elementary HEMT transistors cut off, in the third quadrant of the device characteristic curve.

[0059] According to a possibility illustrated in [Fig. 4B], the anodes of the diodes DS are connected to one or more sensing contacts T'. The sensing contacts T' are independent of the source contacts S'. The sensing contacts T' may correspond to pads arranged between the contact pads S', G', D'. The contacts The sensing contacts T' can be connected via the source finger adjacent to the Schottky contact CS, for example, using a specific 35' connector (vias and metal traces). In this case, several local temperature measurements can be taken via the sensing contacts T' connected to the device's sensors. These measurements can be performed independently of the operation of the individual HEMT transistors.

[0060] Figure 5 illustrates a design plan for a power microelectronic device comprising six blocks L1, L2, L3, L4, L5, L6 of elementary HEMT transistors. A temperature sensor according to the invention has been implanted in block L6 and connected to an independent contact pad T'.

[0061] From the foregoing, it is clear that the present invention makes it possible to integrate one or more precise temperature sensors within a power microelectronic device comprising elementary HEMT transistors. The invention is not limited to the embodiments described above.

Claims

Demands

1. A power microelectronic device comprising: - A plurality of elementary high-electron-mobility transistors (T1, T2, T3) formed on an active layer (11) and connected in parallel, each elementary transistor (T1, T2, T3) comprising a source finger (S), a drain finger (D) and a gate finger (G) interposed between the source finger (S) and the drain finger (D), - A source contact (S') common to the source fingers (S), - A drain contact (D') common to the drain fingers (D), - A gate contact (G') common to the gate fingers (G), the device being characterized in that at least one gate finger is not connected to the gate contact (G') and forms a Schottky contact (CS) with the active layer (11),and in that said at least one gate finger (CS) forms with the adjacent drain finger (D) at least one Schottky diode (DS) configured to measure an operating temperature within the power microelectronic device.

2. Device according to the preceding claim in which at least one grid finger (CS) forming the Schottky contact is connected (35) to the neighboring source finger (S).

3. Device according to the preceding claim in which said neighboring source finger (S) is connected to the source contact (S'), so that the measurement of the operating temperature is made via said source contact (S').

4. Device according to claim 2 comprising at least one sensing contact (T') independent of the source (S'), drain (D') and grid (G') contacts, and in which the neighboring source finger (S) is connected to said at least one sensing contact (T'), so that the measurement of the operating temperature is made via said at least one sensing contact (T').

5. A device according to any one of the preceding claims further comprising a barrier layer (12), for example based on AlGaN, interposed between the active layer (11) and the grid fingers (G), wherein at least one grid finger (CS) forming the Schottky contact passes at least partially through said barrier layer (12).

6. Device according to any one of the preceding claims wherein the at least one gate finger (CS) forming the Schottky contact comprises a plurality of gate fingers (CS) forming with the respective neighboring drain fingers (D) a plurality of Schottky-type diodes (DS) configured to each measure an operating temperature within the power microelectronic device.

7. Device according to the preceding claim comprising a plurality of independent sensing contacts (T'), wherein the grid fingers (CS) of the plurality of Schottky diodes (DS) are connected to said independent sensing contacts (T'), so that the operating temperatures are measured through said sensing contacts (T').

8. Device according to the preceding claim wherein a single sensing contact (T') of the plurality of independent sensing contacts corresponds to a single grid finger (CS) of the plurality of Schottky diodes (DS).

9. Device according to any one of claims 6 to 8 in which the elementary transistors (T1, T2, T3) are arranged in the form of a matrix (L1, L2, L3, L4, L5, L6) and in which the Schottky type diodes (DS) are randomly distributed within said matrix.

10. Device according to any one of claims 6 to 8 in which the elementary transistors (T1, T2, T3) are arranged in the form of a rectangular matrix, said device comprising at least four Schottky diodes (DS) arranged at the four corners of said rectangular matrix.

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