Seal for a joint or juncture – Process of static sealing
Reexamination Certificate
1999-07-16
2002-03-12
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Process of static sealing
C257S688000, C257S693000, C257S788000, C438S112000, C438S127000
Reexamination Certificate
active
06354595
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a process for leaktight sealing of a radiation detector and, more particularly, of a radiological matrix detector of large size consisting of a glass slab covered with amorphous silicon, the amorphous silicon constituting the active material of the elementary detectors of the detection matrix.
It also relates to a radiological radiation detector sealed according to this process.
The invention applies to detectors for radiation with very short wavelengths, and more particularly to the X-radiation used in radiology.
DISCUSSION OF THE BACKGROUND
According to the state of the art, radiation detectors are produced on the basis of a matrix of solid-state photosensitive elements. Known solid-state photosensitive elements are not directly sensitive to rays with very short wavelengths, for example X-rays. It is necessary to combine them with a scintillator component. The latter is made from a substance which has the property, when it is excited by these X-rays, of emitting light in a longer-wavelength range, in the visible spectra (or the near-visible spectrum). The specific wavelength depends on the substance used. The scintillator therefore acts as a wavelength converter. Visible light thus generated is sent to the photosensitive elements which perform photoelectric conversion of the received light energy into electric signals which can be processed by suitable electronic circuits.
A scintillator according to the prior art is described, by way of nonlimiting example, in French Patent Application FR-A-2 636 800 (THOMSON-CSF).
FIGS. 1
a
to
1
e
, appended to the present description, illustrate the mode of operation of a matrix radiation detector of large size according to the prior art, formed by a glass slab covered with amorphous silicon. More particularly,
FIG. 1
e
shows a practical structural example of such a detector. The dimensions of the detector are typically from one or several tens of centimetres side length, it being moreover possible for the detector to be formed by a plurality of glass slabs butted together when the dimensions are particularly large.
FIGS. 1
a
and
1
ba
represent two mutually orthogonal lateral sections of a matrix of photosensitive elements which is conventionally combined with a sheet of scintillating substance.
Each photosensitive element has a photodiode or a phototransistor which is sensitive to photons in the visible spectrum or the near-visible spectrum. By way of example, as illustrated in
FIGS. 1
a
to
1
d
, each photosensitive element consists, for example, of two diodes, D
mn1
and D
mn2
, arranged head-to-tail, and the matrix array RM has column conductors, Cc
1
, to Cc
x
, and row conductors (Cl
1
to Cl
y
. Each of the diodes, D
mn1
and D
mn2
, constitutes, in a known way, a capacitor when it is reverse-biased. The first diode, D
mn1
, has a capacitance typically ten times smaller than the capacitance of the second diode, D
mn2
. It principally fulfils the function of a switch, whereas the second diode is preferentially photodetecting.
At each intersection of a row and of a column, for example of row Cl
n
and column Cc
m
(see
FIG. 1
d
), such a set of two diodes head-to-tail, D
mn1
, and D
mn2
, is arranged. The diodes, made of amorphous silicon, may be replaced by transistors produced using “TFT” technology (Thin Film Transistor), also based on amorphous silicon.
The conductors
12
(
FIGS. 1
a
and
1
b
) are formed by a metal deposit on an insulating substrate
10
, preferably glass, The deposition is followed by a photo-etching operation in order to obtain parallel conductive tracks of suitable width. The diodes (for example Dmn
1
and Dmn
2
) are formed by deposition, on the column conductive tracks
12
, then etching, of the layers of amorphous silicon (aSi) which is-intrinsic or doped using semiconductor materials of the P or N type. A very thin layer of preferably transparent conducting material is deposited on the insulating layer
20
so as to form, after etching, the row conductive tracks
22
of the matrix array RM.
The assembly described above forms what is generally referred to as an “amorphous silicon slab”. The substrate of the slab is in principle glass because of the low cost of this material.
The row conductors, Cl
1
-Cl
x
, and the column conductors, Cc
1
-Cc
y
, constitute the polarization electrodes of the diode capacitors. The latter store electric charges when they are subjected to light radiation and deliver an electric signal, proportional to the stored charge, when they are electrically polarized. The row conductors, Cl
1
-Cl
x
, and the column conductors Cc
1
-Cc
y
, are addressed according to a suitable time sequence so that all the pixels p
mn
are sequentially polarized in a predetermined order. The signal delivered by each pixel p
mn
is thus recovered and processed by electronic circuits (not shown) so as to reconstruct (point by point) the image stored in the form of electric charges.
The signals are recovered in respective connection zones,
3
and
4
, for the rows, Cl
1
-Cl
x
, and the columns, Cc
1
-Cc
y
. The connections to the electronic circuits may be made using flexible multiconductor cables,
30
and
40
, respectively. The flexible multiconductor cables have their ends fixed by adhesive bonding or soldering or, preferably, by hot-pressing to the peripheral connection zones. More precisely, they are usually made using a flexing process, that is to say by hot-pressing an anisotropic conducting film, referred to below as “ACF”, between contact pads located on the glass slab (substrate
10
) and corresponding pads located on an external flexible cable
30
. The conducting pads may be produced on the slab by vacuum deposition. The ACF has the feature of exhibiting electrical conduction after hot-pressing, but only in the axis of the exerted pressure. Along the other axes, the electrical insulation is preserved.
After flexing, the ACF needs to be protected from the external environment in order to preserve its adhesion and electrical-conductivity properties, in particular in severe ambient conditions: humid heat, for example. More generally, whatever the fastening method and the nature of the flexible cable, the end of the flexible multiconductor cable needs to be protected in the connecting zone.
As has been indicated, the photosensitive elements need to be illuminated with visible light (or light in a range close to visible light). It is necessary to provide a scintillator which converts the X-rays into light energy in the visible spectrum. To that end, it is sufficient to cover the above-described amorphous silicon slab with a layer of scintillating substance
24
. By way of example, for a detector sensitive to X-rays of the order of 60 keV, the scintillating substance used is cesium iodide (CsI) doped with sodium iodide (NaI) or with thallium iodide (TiI), depending on whether the intention is to obtain a light signal with wavelength 390 nm or 550 nm, respectively. The layer of scintillating substance
24
is generally produced by a vacuum evaporation. The latter operation is generally followed by annealing of the layer, which allows uniform diffusion of the dopant through the structure made of cesium iodide. The diffusion thus obtained makes it possible to optimize the conversion of the X-rays into visible light.
The simplest method for producing a scintillator consists in depositing a cesium iodide layer on a substrate whose nature is unimportant, of annealing it in order to obtain luminescence properties and of attaching this scintillator assembly to the slab described above. More precisely, this attached scintillator may either be pressed against the slab or optically coupled by adhesive bonding.
The scintillator, which is by nature hygroscopic, absolutely needs to be protected from the external environment, in order to preserve the luminescence properties. This protection may be formed by insulating the scintillator from the external atmosphere by leaktight sealing at the periphery of the substrate
Spinnler Vincent
Vieux Gerard
Knight Anthony
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pickard Alison K.
Thomson Tubes Electroniques
LandOfFree
Method for tight sealing of a radiation detector and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for tight sealing of a radiation detector and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for tight sealing of a radiation detector and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2826986