Stc, Inc

International Standard Electric Corporation

Peter F Blomley

Peter D Scovell

Roger L Baker

Gary J Tomkins

Edward J Whittaker

Peter J Ayliffe

Andrew Paul Lefevre

Kenneth A Arton

Gregory W Yuen

Ewen R Huffman

A fully self-aligned polycrystalline silicon emitter bipolar transistor. Self-alignment of the p.sup.+ base contact (12) is achieved by using oxidized sidewalls (8) (sidewall spacers) of the emitter mesa (7) as part of the p.sup.+ base contact implantation mask. Collector contact (13) alignment can be achieved using oxidized sidewalls (17) of polycrystalline silicon alignment mesas (14) defined in the same polysilicon as the emitter mesa (7) but deposited on oxide (2) rather than the implanted base region (5).

Method of manufacturing a bipolar transistor

A process for fabricating a CMOS compatible bipolar transistor is described. The transistor, which is of the polysilicon emitter type, is fabricated by forming a p-type layer in a well, providing a polysilicon emitter in contact with the layer, using the emitter as a mask to implant p.sup.+ -type base contact regions, and applying contacts to the device.

Method of fabricating a bi-CMOS device

A fully self-aligned polycrystalline silicon emitter bipolar transistor. Self-alignment of the p.sup.+ base contact (12) is achieved by using oxidised sidewalls (8) (sidewall spacers) of the emitter mesa (7) as part of the p.sup.+ base contact implantation mask. Collector contact (13) alignment can be achieved using oxidised sidewalls (17) of polycrystalline silicon alignment mesas (14) defined in the same polysilicon as the emitter mesa (7) but deposited on oxide (2) rather than the implanted base region (5).

Semiconductor devices

A bipolar transistor structure (1) which can be used in an integrated circuit where bipolar (1) and CMOS transistors (2,3) are formed simultaneously on one substrate. In integrated circuit form the material, for example polycrystalline silicon, used for the gates (11,21) of the CMOS transistors is also used for the emitters (29) of the bipolar transistors, the collectors of the bipolar devices are comprised by doped wells (5) in the substrate (4) and the base contacts of the bipolar devices are comprised by regions (27,27a) equivalent to source and drain regions (17,18) of the n-well MOS transistors and bridged by base implants (28). The conventional CMOS processing is modified by the addition of two masking steps and one implant (base implant). One masking step defines the area for the base implant (18) and the other masking step defines an area of the oxide (30) over the base implant which must be removed to allow contact between the polycrystalline silicon (29), which is suitably doped to provide the emitter, and the base ( 27,27a,28). The base contacts are produced in a semi-self-aligned manner.

Method of making Bicmos devices

A drive circuit for a liquid crystal display uses a sampling technique to derive drive signals from a pair of input waveforms. The waveforms comprise positive going and negative going trapezoidal pulses. By sampling the waveforms at appropriate points, single cycle AC signals and zero voltage signals can be provided. The technique subjects the drive circuit to a voltage stress that is lower than that provided by conventional techniques.

Liquid crystal driving systems

A method of manufacturing a bipolar transistor (1) with semi-self-aligned p.sup.+ base contacts (27,27a). A p-type base region (28) is formed in a surface region of an n-type region 5 comprising a collector. An element (29) of, for example, n.sup.+ doped polycrystalline silicon, and comprising an emitter, is formed on the surface in contact with the base region (28). The base contacts (27,27a) are formed by implantation and using the element (29) as a mask. An n.sup.+ collector contact (25) is made to the n-tpe region (5).

A bipolar transistor structure (1) which can be used in an integrated circuit where bipolar (1) and CMOS transistors (2,3) are formed simultaneously on one substrate. In integrated circuit form the material, for example polycrystalline silicon, used for the gates (11,21) of the CMOS transistors is also used for the emitters (29) of the bipolar transistors, the collectors of the bipolar devices are comprised by doped wells (5) in the substrate (4) and the base contacts of the bipolar devices are comprised by regions (27,27a) equivalent to source and drain regions (17,18) of the n-well MOS transistors and bridged by base implants (28). The conventional CMOS processing is modified by the addition of two masking steps and one implant (base implant). One masking step defines the area for the base implant (28) and the other masking step defines an area of the oxide (30) over the base implant which must be removed to allow contact between the polycrystalline silicon (29), which is suitably doped to provide the emitter, and the base ( 27,27a,28). The base contacts are produced in a semi-self-aligned manner.

To provide an adequate dc supply to the electronics of a telephone, when on hook or off hook, there is a transistor (T2) with its emitter-collector path in one line wire, and a storage capacitor (Cpsu) across the input to the telephones's circuits. This capacitor is charged up and maintains dc supply when the line voltage (at A) falls below a preset level. The base of this transistor is connected via another transistor (T1) to the other line wire. The speech output (V.sub.IN) is connected via an operational amplifier (A) to the base of the second transistor (T2). Hence the dc supply and the speech output are in parallel.

Telephone power supply

Method of making a self-aligned bipolar transistor with composite masking

An integrated circuit for a telephone instrument provides the basic (POT) service requirement. The transmit and receive channels of the circuit may be fed via controlled attenuators incorporated in a first ancillary circuit to provide hands-free operation. The circuit also includes a current-limited power supply whereby connection to a second ancillary circuit, including an audio amplifier, may be effected to provide loudspeaker operation.

Telephone instrument circuit

In a loudspeaking telephone it is necessary to ensure that pick-up by the microphone of sound from the loudspeaker does not set up a howling condition. To do this it is usual to disable either the transmitting or the receiving speech channel. To do this, the signal from each channel is applied to an analogue-digital signal envelope converter (30,31), which generates a multi-bit word representative of the current speech amplitude in its channel. Those words are applied to a comparator (32) whose output is indicative of which channel passes speech. Such a converter follows the envelope of the speech signal in its channel to produce the multi-bit word representing the current speech amplitude in its channel. The comparator's output goes via control logic (33) to two attenuators (34, 35), one in each channel. Thus only the channel which is actually passing speech, or the one with the higher speech amplitude, is enabled.

Loudspeaking telephones

Waveform clipping circuits

Gain regulation circuit for an amplifier circuit

A telephone instrument circuit including electronic components for functions such as amplifying incoming and outgoing speech signals. When the electronic transducers of each electronic instruments have to operate in parallel with a carbon microphone in another instrument, problems are likely to arise. To deal with the problem, a voltage regulator is used which includes two essentially series coupled comparator-amplifiers, the first of which is driven by the circuit's supply voltage. The second amplifier has its own reference voltage and its output varies the reference voltage V.sub.R for the first amplifier, whose output is connected to the line whose voltage is being regulated. Above a preset line current, the I-V characteristic of the circuit is almost flat while below the preset threshold it is fairly steep to enable satisfactory parallel operation.

Electronic telephone circuit

A four-transistor bridge amplifier is adapted for use as a bidirectional speech amplifier between a telephone line and an electronic telephone subscriber's instrument. The amplifier is powered from the line and includes two-transistor sections, one or other of which functions dependent on line polarity. The output of the amplifier to the subscriber instrument is taken across a resistor connected between the transistors such that the output always has the same relative polarity whatever the line polarity.

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Bishops Stortford, United Kingdom

Peter F Blomley