KR20020018650A - Electronic devices including micromechanical switches - Google Patents

Abstract

The present invention relates to a method of manufacturing an electronic device comprising an integrated circuit device having a micromechanical switch (10) and a thin film circuit component (20) provided on a common substrate (2). The micro-engineering switch 10 has a contact beam 12 extending over each sacrificial region. The component layer 5 for forming the thin film circuit component is used as a sacrificial region in the region of the substrate assigned to the microengineered switch. This enables the various layers to be shared between the switch and the component. A supplemental support layer 50 may be provided in the contact beam to protect the contact beam from damage during subsequent processing and fabrication steps. This support layer portion may remain attached to the beam at the finished device to increase its strength.

Description

[0001] ELECTRONIC DEVICES INCLUDING MICROMECHANICAL SWITCHES [0002]

Micro-engineering switches have been recognized as capable of providing lower on-resistance and higher off-resistance than conventional semiconductor switching devices than conventional semiconductor switching devices such as transistors or diodes. Other types of microengineered switches have been proposed that utilize either electrostatic or electromagnetic actuation of the movable beam to perform the switching operation. A known method of fabricating a beam of switches involves depositing a beam structure having suitable mechanical and electrical properties on the sacrificial support layer. Eventually, the sacrificial layer is removed to leave a cavity, and when applying an actuation signal, the beam deflects into the cavity. The article entitled " Electrostatic polysilicon micro-relays integrated into MOSFETs " on page 97 of the IEEE 1994 issue of the Microelectronic Systems, A micro relay comprising a beam supported by an end is disclosed. This micro-relay structure is integrated on the transistor substrate, thereby explaining the IC compatibility of micro-engineering devices.

A problem with current methods of fabricating integrated circuit devices including microengineered switches is that the complexity of the fabrication process resulting from other components integrated in the device is increased.

The present invention relates to an electronic device, and more particularly to an integrated circuit device including a microengineered switch and a method of manufacturing the same. In particular, the present invention relates to but not exclusively to an integrated circuit photodiode arrangement in which the individual addressing is controlled by an associated micro-engineering switch.

Figures 1A-1D show processing steps required for the manufacture of an integrated circuit diode structure.

Figures 2A-2E illustrate processing steps of the present invention for the fabrication of microengineered switches that are combined on a substrate, such as the diode structure of Figure 1;

Figure 3 shows a combination of a diode and a microengineered switch as a component laterally adjacent at one location on the substrate.

Figure 4 illustrates the operation of a combined photodiode and a microengineered switch as pixel elements in an image sensor.

5 is a diagram showing a circuit configuration of an image sensor manufactured according to the method of the present invention.

6A to 6G show processing steps of another embodiment of a method for manufacturing an electronic device including a micro-engineering switch and a diode structure on a common substrate.

It should be understood that the figures are only schematic and not proportional scale. In particular, certain dimensions such as the thickness of the layer or area may have been exaggerated, but other dimensions may have been reduced. It is also to be understood that the same reference numerals are used to indicate the same or similar parts throughout the drawings.

According to the present invention there is provided a method of manufacturing an integrated circuit device comprising a plurality of thin film circuit components and a plurality of microengineered switches provided on a common substrate,

Depositing and patterning a lower electrode pattern for the thin film circuit component and defining a bottom contact for the micro-engineering switch,

Depositing and patterning a component layer to form a thin film circuit component on the lower electrode pattern, the component layer defining a sacrificial region over a region of the substrate that is assigned to the micro- Defining the thin film circuit component over a region of the substrate that is assigned to the thin film circuit component;

Depositing and patterning a conductive layer to provide an upper electrode pattern, the upper electrode pattern defining a top contact for the thin film circuit component and defining a contact beam for the micro-engineering switch, Each beam extending over a respective sacrificial region,

Removing the sacrificial region of the component layer to define a space between the contact beam and a lower electrode pattern of each micro-engineering switch,

.

In the method of the present invention, the lower and upper electrode patterns are shared between the micro-engineering switch and the thin film circuit components, thereby reducing the number of additional processing steps required to form the integrated circuit device. Moreover, the layer defining the thin film circuit component also serves as a support for the contact beam of the microengineered switch. In this way, the area of the component layer defines the sacrificial layer of the microengineered switch, whereby the processing steps required for the thin film circuit component and for the switch are shared to the maximum extent possible.

The thin film circuit component may include, for example, a diode that defines a PIN or NIP diode structure, with the top electrode layer overlying the diode structure and in direct contact with the diode structure. Such a diode may be formed of an amorphous silicon layer, and the resulting diode switch integrated circuit device may define pixels of the image sensor.

The top electrode layer may be patterned to define a well in the sacrificial region such that after removal of the sacrificial region, a contact projection is defined at the bottom of the contact beam. This contact protrusion helps to reduce the on-resistance of the switch.

To mechanically support the contact beam, a support layer is deposited and patterned over the component layer in the region of the substrate assigned to the microengineered switch. This may help improve the stiffness of the beam and may prevent breakage of the beam during subsequent etching processes or during dicing and packaging of the integrated circuit components. The removal of the sacrificial layer is preferably carried out with an etchant leaving the support layer, whereby additional support is provided to the contact beam of the article.

An embodiment of an electronic device, in the form of an integrated circuit device, according to the present invention and a method of manufacturing the same will now be described, by way of example, with reference to the accompanying drawings.

This invention relates to integrating micro-engineering switches and other thin-film electronic components into a common substrate. 3, the present invention provides a method of fabricating an electronic device in the form of an integrated circuit device provided with a beam 12 extending over a space 14 in a microengineered switch 10, (12) is selectively movable into the space (14) by applying an actuating signal to close the switch. A beam 12 is deposited over the sacrificial layer and the sacrificial layer is then removed to form the space 14. The present invention provides a method for defining a thin film circuit component 20 from a layer that not only forms the structure of the thin film circuit component 20 but also forms a sacrificial layer that is later removed to form the space 14 do. By way of example, the invention will be described in the context of an integrated circuit image sensor device comprising a photo-diode and a microengineered switch held on a common substrate.

The fabrication process involves depositing and patterning various conductor layers, insulating layers and semiconductor layers on a common substrate by photolithographic techniques. In general, such processes are well known and have been used in the fabrication of wide area thin film electronic devices including arrays of thin film diodes, thin film transistors, etc., which are held on insulating substrates.

The fabrication steps required to form the thin film photo-diode device will first be described in connection with FIG. 1, which shows the processing steps required to form a stacked diode structure. The diode structure itself is generally a conventional shape.

As shown in Fig. 1A, a bottom electro-conductive contact layer 4, preferably made of metal, is provided on an insulating substrate 2 made, for example, of glass. The bottom contact layer 4 may comprise a chrome layer deposited and patterned using conventional thin film processing techniques. A semiconductor layer 5 defining the required diode structure is deposited and patterned directly on the bottom contact layer 4 and a top electrode layer 6 overlying and in direct contact with the top surface of the diode structure ) Followed. The semiconductor layer may be formed of amorphous silicon and may, for example, define NIP or PIN structures. Thus, the semiconductor layer 5 comprises three distinct layers: the bottom layer of the first impurity type, the intrinsic layer, and the top layer of the second opposite impurity type. The top contact layer may comprise ITO, which is transparent and thereby allows the diode to react to light incident from above. The layers 5,6 are patterned together during a single etching step to define the diode structure, as shown in Figure IB.

As shown in FIG. 1C, a passivation layer of a suitable insulating material is used to reduce the edge leakage current at the edge of the diode stack while leaving at least a substantial portion of the top layer 6 region exposed. layer 7 is then deposited and appropriately patterned to surround the diode structure.

This layer 7 may comprise silicon nitride and is again deposited and patterned using conventional techniques.

Finally, as shown in Fig. 1d, an upper contact layer 8 is deposited and patterned to define contact with the top of the top electrode of the diode structure. The layer 8 extends over the surface of the passivation layer 7 in direct electrical contact with the exposed surface of the top electrode layer 6. This includes a metal layer, and as will become apparent from the description below, the nature of the layer, i.e. its composition, thickness, etc., is chosen taking into account the mechanical and electrical requirements of the microengineered switch. FIG. 1D shows one complete diode structure that provides a thin film circuit component 20 with another, co-formed diode structure to be integrated on a common substrate together with a micro-engineering switch.

The technique used for depositing and patterning the various layers is such a known kind that has been conventionally used to fabricate thin film electronic devices on insulating substrates to produce wide area electronic devices, Typically followed by deposition and subsequent patterning by a photolithography process. It is not considered necessary to describe these processes as such in detail herein.

Figures 2A-2E illustrate processing steps for the manufacture of a microengineered switch when a microengineered switch is provided integrated on a substrate such as the diode of Figures 1A-1D. Deposition and patterning of the layers performed in Figures 2a, 2b, 2d correspond to the deposition and patterning of the layers in Figure 1a, 1b, 1d, so that the diodes and switches are suitably interconnected, The same layer deposition and patterning process.

2A, the deposited metal layer constituting the bottom contact layer 4 is patterned to define the inter-spaced switch contacts 16A, 16B of the micro-engineering switch as well as the intermediate control electrode 16C. do. The sacrificial region is formed at the location of each micro-engineering switch extending above the contact by depositing and patterning the constituent layers that make up the diode stack 5,6 of Figure 2b.

Figure 2c shows the processing steps required for a microengineered switch only. This step includes etching the opening 17 through the upper electrode layer 6 of the diode layer structure deposited in one of the switch contacts, i. E., Directly over the contact 16B. Fig. 2c can precede or follow Fig. 1c. Also, Figure 1c does not play any role in the fabrication of microengineered switch structures.

2D, the deposited top metal contact layer 8 forms the contact beam 12 when patterned. An upper contact layer 8 region extending into the recess 17 defines a contact protrusion 18 on the bottom surface of the contact beam 12.

At the microengineering switch position, the portions of the layers 5, 6 constituting the sacrificial region are removed by etching. The structure shown in FIG. 2E is obtained by etching not only an amorphous silicon layer defining the diode structure but also the upper ITO contact layer 6 of this region. The free-space space for creating the free-space space 14 by removing these layers is such that when applying or removing an operating voltage to the contact 16C, the area overlying the contact 16A through the layer 8, Thereby making or breaking electrical contact between the switch electrodes 16A and 16B.

During sacrificial layer etching to generate the structure shown in Figure 2E, the layer defining photodiode 20 is protected from etchant while being used by a suitable photomask. The removal of the sacrificial layer region is preferably performed using a wet etch because the liquid can penetrate into all regions of the space 14. This is also a relatively inexpensive and safe process compared to alternative dry and vapor etching techniques. Of course, the selected etchant should be selected accordingly since the metal contact beam 12 and the electrode 16 should be unaffected.

The use of integrated circuit devices that incorporate diodes and micro-engineering switches into image sensors will now be described. A conventional wide area, thin film integrated circuit image sensor array using photodiodes comprises an array of image sensor pixels, each pixel in the array of image sensor pixels comprising a photodiode and a switching diode (protected from incident light) Lt; RTI ID = 0.0 > (TFT). ≪ / RTI >

The microengineered switch fabricated using the method of the present invention is used as a switching element in the image sensor photodiode array. In this case, each image sensor pixel includes a photodiode and associated microengineered switch to control the passage of charge from or to the photodiode to enable addressing of the image sensor array. This is achieved by electrically interconnecting the beam 12 with the top contact 8, where the photodiode and the switch are formed integrally.

Reduced on-resistance and increased off-resistance, which can be achieved using micro-engineering switches, enable an increase in the amount of charge stored on the photodiode that can be read, thereby causing some charge In the so-called memory effect that remains on the photodiode. The use of microengineered switches also makes it possible to reduce the output capacity of the device compared to TFTs or switching diodes that further improve the operational performance of the image sensor arrangement. Microengineered switches also do not have photosensitivity, thereby eliminating the need to protect such devices from incident optical signals.

Figure 3 shows a thin-film diode 20 and a micro-engineering switch (not shown) which define individual pixel circuit structures in which a micro-engineering switch is electrically connected in series with the photodiode through a contact layer 8 and a metal layer constituting the beam 12. [ 10) side by side. It will be readily appreciated that the same reference numerals as in Figs. 1 and 2 are used and that the layer is shared between the two devices 10,20. Figure 3 also shows a selective protective layer 19 for protecting the micro-engineering switch 10 in the final device. This layer 19 comprises a preformed glass microsheet mounted on the flat top surface of the portion 11 of the top contact layer 8 on the passivation layer 7 functioning as a spacer can do.

In its original state, the position of the beam 12 of the microengineered switch is such that the contacts 16A and 16B are electrically disconnected as shown in Fig. 3 so that the switch is effectively open. When the operating voltage signal is applied to the electrode 16C, the beam 12 is pivoted down by the electrostatic attraction effect so that the projection 18 of the beam 12 contacts the electrode 16B, thereby closing the switch, (16A, 16B) are electrically connected. When the actuation signal is removed, the beam returns to its original, loosened structure. As a typical example, the beam may be about 20 microns in length, the gap between the protrusion 18 and the electrode 16B is about 1.5 microns in a relaxed state, and the size of the pivotal defection of the beam is It is about 8 degrees.

Figures 4 and 5 illustrate the use of the diode-switch arrangement of Figure 3 in an image sensor. Figure 4 illustrates the basic operating principle of an image sensor using a photodiode as the light detecting element.

As shown in Fig. 4, the electromagnetic radiation R is incident on a photosensitive diode 30 responsive to electromagnetic radiation R, which may include visible light. The single photo sensitive element is shown in Figure 4 as being in parallel with the capacitor 32 that may exhibit parasitic or self-capacitance of the diode 30 or may be used to enhance the dynamic range of the detector And may include additional capacitors. The cathode 30a of the diode is connected to the common line 34 while the anode 30b of the diode 30 is connected to the first terminal of the associated switching element 36. [ The second terminal of the switch 36 is connected to the read amplifier 38. The circuit of Figure 4 shows a component placement diagram for a single image sensor pixel.

One possible drive scheme that allows the circuit of FIG. 4 to provide an output representing the incident light on the photodiode will now be described.

At the beginning of the address period the switch 36 is closed and the capacitor 32 is charged to an initial value which is determined by the difference between the voltage at the terminal 34 and the voltage provided by the amplifier 38. For example, the terminal 34 may be at 5 volts while the amplifier drives the photodiode anode at zero volts. The photodiode capacitor 32 is thereby charged to an initial voltage of 5 volts, and the photodiode is reverse-biased. During a subsequent light sensing operation, the switch 36 is opened such that no current can flow to or from the terminal 34. During this time, the light incident on the photodiode 30 causes the production of a minority carrier (photo) current which is responsible for the discharge of the capacitor 32, indicated by arrow 39. At the end of the photodetection operation, the voltage across the photodiode will drop as a function of the intensity of the incident light. To measure the amount of voltage drop, the switch 36 is closed again and the current flowing from the terminal 34 to recharge the capacitor 32 is measured by the amplifier 38.

There are a variety of alternative pixel structures and driving structures, which will be apparent to those skilled in the art. Essentially, the switch 36 needs to allow the photodiode to be electrically disconnected so that the discharge of the photodiode capacitance occurs during the photodetection period.

Fig. 5 shows an implementation of the pixel structure of Fig. 4 in a wide area two-dimensional image sensor arrangement with a micro-engineering switch 10 acting as a switch 36. Fig. This arrangement includes rows and columns of individual pixels and each pixel is electrically connected in series between the common terminal 34 shared by all the pixels and the charge sensitive read amplifier 38 A photodiode 20 and a micro-engineering switch 10. The row driver circuit 40 is provided to generate an actuating signal applied to the electrode 16C of the microengineered switch to open and close the switch. As in the prior art, the pixels of the array are sequentially addressed one row at a time. The pixels have a pitch of typically 200 mu m and the arrangement can be up to 400 mm x 400 mm to obtain the required resolution where the image detector can be used to detect diagnostic x-ray images of human or animal body regions Lt; / RTI > Typically, although only a portion of the array is shown in FIG. 5 for clarity, the array may be a 2,000x2,000 array of pixels. In the case of a x-ray image detector, the electromagnetic radiation R can be supplied from an energy conversion layer (not shown) which has x-radiation as input and provides visible light that is detected by the diode as an output have. In such a case, the energy conversion layer may be a phosphor layer, for example a thallium-doped cesium iodide.

Apart from the use of micro-engineering switches for the pixel active matrix switching function, the arrangement is generally similar to the known type of image sensing arrangement which uses a photodiode in terms of its general mode of operation.

It will be appreciated that the address lines interconnecting the pixels with the circuits 40, 38 and the common terminal 34 are formed from a conductive material deposited on the substrate. The switch control electrode 16C may thus include an integral extension of a set of row address conductors defined from a deposited metal layer such as that used for the bottom contact layer 4 of the photodiode. The set of column address conductors has an integral extension extending from the layer being used to provide another deposited conductive layer, for example the top contact layer 8, the bottom contact of the photodiode being connected to the first set, 16B may similarly be formed by suitably patterning the layer with an integral extension connected to the second set. An insulating material is provided at their intersection between the row and the set of thermal conductors and this can be provided by the material deposited to form the passivation layer (7).

With regard to the process described in connection with Figs. 2A-2E, problems may arise as a result of the wet etch used to form the space 14 shown in Fig. 2E in some circumstances. The liquid used in the wet etching process is viscous, which causes the beam 12 to bow or break as it moves in the liquid. Drying can also be problematic because the water used in the cleaning action tends to form a bead when the water becomes smaller as the water is left under the beam 12 to dry and the surface tension deforms the beam to be. The beam 12 may also be subject to physical damage when the wide area arrangement of the device is diced and packaged and interconnects are formed at the edge of the integrated circuit device. The material for the beam 12 should not only be compatible with the large area used, the thin film processing, but also the electrical requirements that define the electrical properties of the switch, as well as the electrical requirements for the correct deformation of the beam 12 The mechanical requirements also have to be met, which presents difficulties in solving these problems.

Other embodiments of the microengineered switch and its fabrication method will now be described and the additional method steps of fabricating the microengineered switch in conjunction with the embodiment and fabricating method in which Figures 6A-6G contribute to solving any of the above problems For example. The steps described with reference to Figures 2A and 2B are performed first to define the switch region as a patterned sacrificial layer. A support layer 50 of dielectric material is then deposited and patterned over the sacrificial layer of the switch to mechanically support the contact beam. FIG. 6A shows a cross-sectional view taken along line A-A of FIG. 6B, and FIG. 6B shows a plan view at this stage of the fabrication process. As can be seen from the above plan view, the support layer 50 extends over the outer circumferential edge of the sacrificial layer, here the reference numeral 52 '. The layer 52 corresponds to layer 5 of the previous embodiment. The support layer 50 is provided with a series of openings 54 that completely pass through the support layer, as will become apparent below, the series of openings is such that a wet etchant approaches the sacrificial layer 52 But above the sacrificial layer 52, away from the intended position of the contact beam. The support layer 50 is also provided with additional openings 56 aligned with the contact electrodes 16c which are used to form the contact protrusions 18 described with reference to Figure 2D .

Fig. 6C corresponds to Fig. 2C where recesses 17 are provided in the top contact layer 6, but this time using the support layer 50 as a mask when etching through the openings 56. Fig.

The upper contact layer 8 is formed as previously described and becomes the structure shown in Figure 6D after removing the sacrificial layer using wet etching. The etchant is selected to remove the ITO top contact layer and the amorphous silicon layer of the diode structure that make up the sacrificial layer and leave the support layer 50 in place. This support layer preferably comprises silicon nitride having a greater stiffness than the metal of the top contact layer 8. After removal of the sacrificial layer 52, the support layer substantially defines a cradle that supports the contact beam 12. The cradles extend laterally up to the outer circumferential wall 50 which extends below the contact beam 12 and which bridges the space 14 between the contact beam 12 and the substrate 2 from the contact beam 12 Extend. As shown in the top view of Figure 6E, the cradles remain untouched at this stage so that the upper and lower edges 50a, 50b shown in Figure 6e, as well as the end edges 50c seen in the cross-section of Figure 6d, As shown in FIG.

These cradles can be held in place during dicing and packaging of the integrated circuit components and during formation of the interconnects. Alternatively, the cradles can be removed after completing the wet etch process to remove the sacrificial layer. The cradles can be removed by reactive ion etching while the contact beam 12 acts as a mask. Any material of the support layer 50 underlying the contact beam 12 will not be removed by this reactive ion etching treatment so that the support layer can be held directly beneath the beam, And the control electrode 16c used for electrostatic operation, as well as providing a reinforcement for the beam. FIG. 6F is a plan view showing the structure of a micro-engineering switch after reactive ion etching of crayers, and FIG. 6G is a sectional view of the structure.

A microengineered switch similar to that coupled to the photodiode may be used to form a switching device in the row driver circuit 40 or the charge sensitive amplifier 38, for example as a component of a shift register circuit It can also be used. In this case, the circuit can be integrated on a substrate such as an image sensor array and can be fabricated in the same manner as the pixel switch and simultaneously with the pixel switch 10 from the same deposition layer. Alternatively or additionally, multiplexing circuitry may be provided between the row driver circuit 40 and an array of pixels and between the amplifier 38 and an array of pixels. Such a multiplexing circuit can also be similarly integrated in a substrate, such as a pixel in an array, and again comprise a microengineered switch of the same design.

Although the invention has been described with particular reference to an image sensor pixel structure comprising a series connected diode and a switch, the present invention can be applied to many other electronic devices including integrated circuit devices. Similarly, although one particular pixel design is shown for an image sensor, it will be apparent to those skilled in the art that there can be many other possibilities. Image sensors using pixels with micro-engineering switches and photodiodes fabricated using the method of the present invention are useful, for example, for x-ray image sensors, document scanners or fingerprint sensors or many other applications where optical images are captured . The method of the present invention enables a reduction in the number of masks required in the fabrication process of an integrated circuit device and improves the performance of the device compared to many conventional switch designs.

Various alternatives to the specific materials described in this patent application will be apparent to those skilled in the art. Deposition and patterning processes have not been described in detail in this application because such embodiments are also evident to those skilled in the art of thin film integrated circuit design.

As described above, the present invention is applied to an electronic device, and more particularly to an integrated circuit device including a micro-engineering switch and a method of manufacturing the same.

Claims (12)

CLAIMS 1. A method of fabricating an integrated circuit device comprising a plurality of micromechanical switches and a plurality of thin film circuit components provided on a common substrate, Depositing and patterning a lower electrode pattern for the thin film circuit component and defining a bottom contact for the micro-engineering switch, Depositing and patterning a component layer to form the thin film circuit component on the lower electrode pattern, the component layer defining a sacrificial region over an area of the substrate that is assigned to the micro- And defining the thin film circuit component over a region of the substrate that is assigned to the thin film circuit component; Depositing and patterning a conductive layer to provide an upper electrode pattern, the upper electrode pattern defining a top contact for the thin film circuit component and defining a contact beam for the micro-engineering switch, Each of the contact beams extending over a respective sacrificial area; Removing the sacrificial region of the component layer to define a space between the contact beam and the lower electrode pattern of each micro- / RTI > The method of claim 1, wherein the thin film circuit component comprises a diode. 3. The method of claim 1 or 2, wherein the component layer defines a PIN or NIP diode structure and a top electrode layer. 4. The method of claim 3, wherein an amorphous silicon layer is deposited to define the diode structure. 5. The method of claim 3 or 4, wherein the upper electrode layer is patterned to define a well in the sacrificial region so that after the sacrificial region is removed, the contact protrusions are confined to the bottom surface of the contact beam . 6. The method according to any one of claims 1 to 5, further comprising the step of depositing a passivation layer around the patterned component layer constituting the thin film circuit component. 7. The method of any one of claims 1 to 6, wherein the upper electrode pattern is patterned to define a cantilevered beam structure for each micro-engineering switch. 8. A device according to any one of the preceding claims, wherein a support layer is deposited and patterned on the component layer in the region of the substrate assigned to the micro-engineering switch to mechanically support the contact beam , Way. 9. The method of claim 8, wherein the removal of the sacrificial region is performed using an etchant that leaves the support layer. 10. The method of claim 9, wherein, after removing the sacrificial region, the support layer includes a contact beam, which is masked with a mask, to leave a portion forming a strengthening layer extending from immediately below the contact beam. Wherein the first etchant is further etched using the second etchant. An image sensor comprising an array of pixels, Each pixel comprising a photodiode and a microengineered switch, wherein the image sensor device is manufactured using the method of any one of claims 1 to 10. An image sensor device according to claim 11 for detecting incident X-ray radiation, And a conversion layer for converting incident X-ray radiation into optical radiation for detection by a photodiode of the image sensor device.